[NFC][Support] Refactor FormatVariadic code. (#106610)

- Rename `Align` field in ReplacementItem/FmtAlign to `Width` to 
  accurately reflect its use.
- Change both `Width` and `Index` in ReplacementItem to 32-bit int 
  instead of size_t (as 64-bits seems excessive in this context).
- Eliminate the use of `Empty` ReplacementType, and use the
  existing std::optional<> instead to indicate that.
- Eliminate some boilerplate type code in formatv().
- Eliminate the loop in `splitLiteralAndReplacement`. The existing
  code will never loop back.
- Directly use constructor instead of std::make_pair.

0 files changed, 0 insertions, 0 deletions