tbv2: fix thrift isset with ClangTypeParser

[JakeHillion]

tbv2: fix thrift isset with ClangTypeParser

Some of the logic that makes Thrift isset work for TreeBuilder-v2 in DrgnParser (JIT OIL) wasn't ported to ClangTypeParser meaning it doesn't work in Ahead-of-Time (AoT) OIL.

Add the template parameter name reconstruction for enum values to ClangTypeParser.

Test plan:

• Tested with Thrift isset enabled on an internal type. Doesn't build before, does build after.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (40af807) 62.42% compared to head (d47fae1) 62.42%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #463 +/- ## ======================================= Coverage 62.42% 62.42% ======================================= Files 123 123 Lines 12054 12054 Branches 1965 1965 ======================================= Hits 7525 7525 Misses 3577 3577 Partials 952 952 ```

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