[clang] [clang-format] Add an option to format integer and float literal case (PR #151590)

[Andy MacGregor via cfe-commits]

30Wedge wrote:

> IMO, the best place to handle this is in FormatTokenLexer::getNextToken(). 

I see you have much more experience in this part of the codebase, but I have some hangups because I don't understand the implications of doing this move myself. Here's what I'm thinking; are these valid concerns?

The  `FormatTokenLexer` class seems like it does the work of parsing a file into tokens for use downstream by all of the other formatters. What are the implications of running `NumericLiteralCaseFixer` or any other reformatting at this stage for all consumers? Do consumers of lexed `FormatTokens` assume they are receiving a faithful representation of the underlying file? Are there architecture issues regarding separation of concerns that come up if we do formatting directly in the lexing stage?

Separately, I think that all classes that subclass `TokenAnalyzer` and use `TokenAnalyzer::process()` would wind up calling `FormatTokenLexer::lex()` -- which would end up running `NumericLiteralCaseFixer` reformatting redundantly for each other pass. Please correct me if I'm reading this wrong. 
I could see how that is still lower overhead than adding a totally separate pass, but it still seems odd to run the same reformatting function many separate times in unrelated passes.
Maybe it would be better to add  `NumericLiteralCaseFixer`  into some other existing pass instead?

https://github.com/llvm/llvm-project/pull/151590