[clang] [clang] Factor out OpenACC part of `Sema` (PR #84184)

[Vlad Serebrennikov via cfe-commits]

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@@ -1162,6 +1162,11 @@ class Sema final {
   /// CurContext - This is the current declaration context of parsing.
   DeclContext *CurContext;
 
+  SemaOpenACC &OpenACC() {
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Endilll wrote:

I'm not too keen to adhere to our style guide here, as this adds noise for users on top of already more lengthy notation: this PR made the following usage
`getActions().ActOnOpenACCClause(Kind, ClauseLoc);` to look like this:
`getActions().OpenACC().ActOnClause(Kind, ClauseLoc);`. If we adhere to style guide, it's going to become
`getActions().getOpenACC().ActOnClause(Kind, ClauseLoc);` without any benefit for readers and writers of the code.

https://github.com/llvm/llvm-project/pull/84184