[clang][Preprocessor] Add peekNextPPToken, makes look ahead next token without side-effects (#143898)

This PR introduce a new function `peekNextPPToken`. It's an extension of
`isNextPPTokenLParen` and can makes look ahead one token in preprocessor
without side-effects.

It's also the 1st part of
https://github.com/llvm/llvm-project/pull/107168 and it was used to look
ahead next token then determine whether current lexing pp directive is
one of pp-import or pp-module directive.

At the start of phase 4 an import or module token is treated as starting
a directive and are converted to their respective keywords iff:

 - After skipping horizontal whitespace are
    - at the start of a logical line, or
    - preceded by an export at the start of the logical line.
- Are followed by an identifier pp token (before macro expansion), or
    - <, ", or : (but not ::) pp tokens for import, or
    - ; for module
Otherwise the token is treated as an identifier.

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Signed-off-by: yronglin <yronglin777@gmail.com>

0 files changed, 0 insertions, 0 deletions