Add Decimal.TryFormat span-based method (#15145)

* Move decimal formatting to managed code

- Move decimal formatting to shared (decimal itself is still not shared)
- Delete VM's decimal formatting code

* Add Decimal.TryFormat span-based method

* Workaround ProjectN compiler bug

Apply the same attribution that's applied to the code in corert.

* Address PR feedback

* Temporarily undo explicit layout change

Seeing whether it's the cause of these failures on Unix (Ubuntu, CentOS, and OSX):
```
JIT.Directed.coverage.oldtests.lclfldadd_cs_r.lclfldadd_cs_r
JIT.Directed.perffix.primitivevt.mixed1_cs_ro.mixed1_cs_ro
JIT.Methodical.fp.exgen.1000w1d_cs_r.1000w1d_cs_r
JIT.Methodical.fp.exgen.1000w1d_cs_ro.1000w1d_cs_ro
JIT.Methodical.fp.exgen.1000w1d_cs_do.1000w1d_cs_do
JIT.Methodical.fp.exgen.1000w1d_cs_d.1000w1d_cs_d
JIT.Methodical.fp.exgen.10w5d_cs_d.10w5d_cs_d
JIT.Methodical.fp.exgen.10w5d_cs_do.10w5d_cs_do
JIT.Methodical.fp.exgen.10w5d_cs_ro.10w5d_cs_ro
JIT.Methodical.fp.exgen.200w1d-02_cs_do.200w1d-02_cs_do
JIT.Methodical.fp.exgen.10w5d_cs_r.10w5d_cs_r
JIT.Methodical.fp.exgen.200w1d-02_cs_ro.200w1d-02_cs_ro
JIT.Directed.perffix.primitivevt.mixed1_cs_do.mixed1_cs_do
```

Example failure:
```
FAILED   - JIT/Methodical/fp/exgen/200w1d-02_cs_ro/200w1d-02_cs_ro.sh
               BEGIN EXECUTION
               /mnt/j/workspace/dotnet_coreclr/master/checked_ubuntu_tst_prtest/bin/tests/Windows_NT.x64.Checked/Tests/coreoverlay/corerun 200w1d-02_cs_ro.exe

               Unhandled Exception: System.OverflowException: Value was either too large or too small for an Int32.
                  at System.Convert.ThrowInt32OverflowException()
                  at System.Convert.ToInt32(Int64 value)
                  at testout1.Func_0()
                  at testout1.Main()
               ./200w1d-02_cs_ro.sh: line 243: 101339 Aborted                 (core dumped) $_DebuggerFullPath "$CORE_ROOT/corerun" $ExePath $CLRTestExecutionArguments
               Expected: 100
               Actual: 134
               END EXECUTION - FAILED
```

4 files changed, 0 insertions, 68 deletions

diff --git a/src/classlibnative/bcltype/decimal.cpp b/src/classlibnative/bcltype/decimal.cpp
index ed63391e54..c338e5d0c3 100644
--- a/src/classlibnative/bcltype/decimal.cpp
+++ b/src/classlibnative/bcltype/decimal.cpp
@@ -288,33 +288,6 @@ FCIMPL1(void, COMDecimal::DoTruncate, DECIMAL * d)
 }
 FCIMPLEND
 
-
-void COMDecimal::DecimalToNumber(DECIMAL* value, NUMBER* number)
-{
-    WRAPPER_NO_CONTRACT
-    _ASSERTE(number != NULL);
-    _ASSERTE(value != NULL);
-
-    wchar_t buffer[DECIMAL_PRECISION+1];
-    DECIMAL d = *value;
-    number->precision = DECIMAL_PRECISION;
-    number->sign = DECIMAL_SIGN(d)? 1: 0;
-    wchar_t* p = buffer + DECIMAL_PRECISION;
-    while (DECIMAL_MID32(d) | DECIMAL_HI32(d)) {
-        p = COMNumber::Int32ToDecChars(p, DecDivMod1E9(&d), 9);
-        _ASSERTE(p != NULL);
-    }
-    p = COMNumber::Int32ToDecChars(p, DECIMAL_LO32(d), 0);
-    _ASSERTE(p != NULL);
-    int i = (int) (buffer + DECIMAL_PRECISION - p);
-    number->scale = i - DECIMAL_SCALE(d);
-    wchar_t* dst = number->digits;
-    _ASSERTE(dst != NULL);
-    while (--i >= 0) *dst++ = *p++;
-    *dst = 0;
-    
-}
-
 int COMDecimal::NumberToDecimal(NUMBER* number, DECIMAL* value)
 {
     WRAPPER_NO_CONTRACT
diff --git a/src/classlibnative/bcltype/decimal.h b/src/classlibnative/bcltype/decimal.h
index 6ce1fbe677..b932420bde 100644
--- a/src/classlibnative/bcltype/decimal.h
+++ b/src/classlibnative/bcltype/decimal.h
@@ -43,7 +43,6 @@ public:
     static FCDECL1(INT32, ToInt32, FC_DECIMAL d);	
     static FCDECL1(Object*, ToString, FC_DECIMAL d);
     
-    static void DecimalToNumber(DECIMAL* value, NUMBER* number);
     static int NumberToDecimal(NUMBER* number, DECIMAL* value);
     
 
diff --git a/src/classlibnative/bcltype/number.cpp b/src/classlibnative/bcltype/number.cpp
index e399c82f63..eea2b2e60b 100644
--- a/src/classlibnative/bcltype/number.cpp
+++ b/src/classlibnative/bcltype/number.cpp
@@ -2009,45 +2009,6 @@ ParseSection:
 #pragma warning(pop)
 #endif
 
-FCIMPL3_VII(Object*, COMNumber::FormatDecimal, FC_DECIMAL value, StringObject* formatUNSAFE, NumberFormatInfo* numfmtUNSAFE)
-{
-    FCALL_CONTRACT;
-
-    NUMBER number;
-
-    wchar fmt;
-    int digits;
-
-    STRINGREF  refRetVal = NULL;
-    HELPER_METHOD_FRAME_BEGIN_RET_1(refRetVal);
-
-    struct _gc
-    {
-        STRINGREF   format;
-        NUMFMTREF   numfmt;
-    } gc;
-
-    gc.format = (STRINGREF) formatUNSAFE;
-    gc.numfmt = (NUMFMTREF) numfmtUNSAFE;
-
-    if (gc.numfmt == 0)
-        COMPlusThrowArgumentNull(W("NumberFormatInfo"));
-
-    COMDecimal::DecimalToNumber(&value, &number);
-
-    fmt = ParseFormatSpecifier(gc.format, &digits);
-    if (fmt != 0) {
-        refRetVal = NumberToString(&number, fmt, digits, gc.numfmt, TRUE);
-    } else {
-        refRetVal = NumberToStringFormat(&number, gc.format, gc.numfmt);
-    }
-
-    HELPER_METHOD_FRAME_END();
-
-    return OBJECTREFToObject(refRetVal);
-}
-FCIMPLEND
-
 FCIMPL3_VII(Object*, COMNumber::FormatDouble, double value, StringObject* formatUNSAFE, NumberFormatInfo* numfmtUNSAFE)
 {
     FCALL_CONTRACT;
diff --git a/src/classlibnative/bcltype/number.h b/src/classlibnative/bcltype/number.h
index 77f902fb41..e9651b66a1 100644
--- a/src/classlibnative/bcltype/number.h
+++ b/src/classlibnative/bcltype/number.h
@@ -31,7 +31,6 @@ struct NUMBER {
 class COMNumber
 {
 public:
-    static FCDECL3_VII(Object*, FormatDecimal, FC_DECIMAL value, StringObject* formatUNSAFE, NumberFormatInfo* numfmtUNSAFE);
     static FCDECL3_VII(Object*, FormatDouble,  double  value, StringObject* formatUNSAFE, NumberFormatInfo* numfmtUNSAFE);
     static FCDECL3_VII(Object*, FormatSingle,  float   value, StringObject* formatUNSAFE, NumberFormatInfo* numfmtUNSAFE);
     static FCDECL2(FC_BOOL_RET, NumberBufferToDecimal, BYTE* number, DECIMAL* value);