[rust] Make enum names public (#5690)

* Bugfix for Rust generation of union fields named with language keywords

Looking at ParseField, it appears that in the case of unions, an extra field with a `UnionTypeFieldSuffix` is added to the type definition, however, if the name of this field is a keyword in the target language, it isn't escaped.

For example, if generating code for rust for a union field named `type`, flatc will generate a (non-keyword escaped) field named `type_type` for this hidden union field, and one (keyword escaped) called `type_` for the actual union contents.

When the union accessors are generated, they refer to this `type_type` field, but they will escape it mistakenly, generating code like this:

```
  #[inline]
  #[allow(non_snake_case)]
  pub fn type__as_int(&self) -> Option<Int<'a>> {
    if self.type__type() == Type::Int {
      self.type_().map(|u| Int::init_from_table(u))
    } else {
      None
    }
  }
```

Which will fail to build because the field is called `self.type_type()`, not `self.type__type()`.

* [Rust] Add crate-relative use statements for FBS includes.

At present if a flatbuffer description includes a reference to a type in
another file, the generated Rust code needs to be hand-modified to add
the appropriate `use` statements.

This assumes that the dependencies are built into the same crate, which
I think is a reasonable assumption?

* Revert "[Rust] Add crate-relative use statements for FBS includes."

This reverts commit d554d79fecf5afd6da6fb993b30b4cd523a5889a.

* Address comments raised in PR

* Update documentation comments per feedback

* Fix typo

* [rust] Make enum variant names public.

* Update generated test files

* Add test for public enum names

1 files changed, 1 insertions, 1 deletions

diff --git a/src/idl_gen_rust.cpp b/src/idl_gen_rust.cpp
index 01a2cbbd..6aaaddea 100644
--- a/src/idl_gen_rust.cpp
+++ b/src/idl_gen_rust.cpp
@@ -621,7 +621,7 @@ class RustGenerator : public BaseGenerator {
     static const uint64_t kMaxSparseness = 5;
     if (range / static_cast<uint64_t>(enum_def.size()) < kMaxSparseness) {
       code_ += "#[allow(non_camel_case_types)]";
-      code_ += "const ENUM_NAMES_{{ENUM_NAME_CAPS}}:[&'static str; " +
+      code_ += "pub const ENUM_NAMES_{{ENUM_NAME_CAPS}}:[&'static str; " +
                NumToString(range + 1) + "] = [";
 
       auto val = enum_def.Vals().front();