[clang] [Clang] Improve diagnostic of Microsoft integer literals and refactor its truncation logic (PR #212743)

[A. Jiang via cfe-commits]

frederick-vs-ja wrote:

I think we should make this PR just fix crash, which should be uncontroversial.

I've just verified that MSVC supports up to `18446744073709551615i8`. The same limit, 2<sup>64</sup>-1, is applied to all `iN` and `uiN` extended literal suffixes. Maybe it's better to do same as MSVC (i.e. truncating) at this moment.

FWIW, I reported https://developercommunity.visualstudio.com/t/11127972 to suggested MSVC to emit warnings.

https://github.com/llvm/llvm-project/pull/212743