[clang-format] Add an option to format numeric literal case (#151590)

Some languages have the flexibility to use upper or lower case
characters interchangeably in integer and float literal definitions.

I'd like to be able to enforce a consistent case style in one of my
projects, so I added this clang-format style option to control it.

With this .clang-format configuration:
```yaml
    NumericLiteralCaseStyle:
      UpperCasePrefix: Never
      UpperCaseHexDigit: Always
      UpperCaseSuffix: Never
```

This line of code:
```C
    unsigned long long  0XdEaDbEeFUll;
```

gets reformatted into this line of code:
```C
    unsigned long long 0xDEAFBEEFull;
```

-----

I'm new to this project, so please let me know if I missed something in
the process. I modeled this PR from
[IntegerLiteralSeparatorFixer](https://reviews.llvm.org/D140543)

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