[clang-tools-extra] [clang-tidy][NFC] Convert Lexer utils to use std::optional<Token> (PR #174809)

[via cfe-commits]

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@@ -21,10 +21,13 @@ class Stmt;
 
 namespace tidy::utils::lexer {
 
-/// Returns previous token or ``tok::unknown`` if not found.
-Token getPreviousToken(SourceLocation Location, const SourceManager &SM,
-                       const LangOptions &LangOpts, bool SkipComments = true);
-std::pair<Token, SourceLocation>
+/// Returns previous token.
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zeyi2 wrote:

A minor nit:

```suggestion
/// Returns previous token or ``std::nullopt`` if not found.
```

but TBH I don't have a strong opinion for this :)

https://github.com/llvm/llvm-project/pull/174809