And apply throughout the code base.

Allow an option to leave preprocessor directive indenting as-is. This
simplifies handling mixed styles of CPP directive indentation.

Fixes #38511

Fix #145161

Also set it to SIEB_Always for WebKit style.

Closes #85525.
Closes #93635.

Before this commit, when `LineJoiner` joins a line with affected leading
whitespace, it would drop the knowledge of this entirely. However, when
the `AffectedRangeManager` is computing the affected lines, the leading
empty whitespace lines are potentially considered for non-first tokens
in the `AnnotatedLine`. This causes a discrepancy in behavior when an
`AnnotatedLine` is put together from joining multiple lines versus when
it is not.

We change `LineJoiner::join` to follow `AffectedRangeManager`'s logic,
considering the leading whitespace when determining `Affected` for a
token.


https://github.com/llvm/llvm-project/blob/a63f57262898588b576d66e5fd79c0aa64b35f2d/clang/lib/Format/AffectedRangeManager.cpp#L111-L130

Fixes #138942.

Fix #62356

Fixes #136266

Fix #51940

Also remove redundant name qualifiers format::, FormatStyle::, and
LanguageKind::.