[lldb][CompilerType] Add CompilerType::IsRealFloatingPointType (#178904)

This is part of a patch series to clean up the
`TypeSystemClang::IsFloatingPointType` API. Currently the API is a bit
of a foot-gun because it returns `true` for both Complex floats and
vector types whose element types are floats, but most call-sites
probably don't handle these correctly. The former aligns with the
`clang::Type::isFloatingType` API, but the latter doesn't. This specific
implementation choice will be addressed in a separate patch. This patch
adds a new `CompilerType::IsRealFloatingPointType` API which clients can
use to query about non-complex floats (named after the similarly named
`clang::Type::isRealFloatingType`).

This allows us to clean up some of the callers which only wanted to
handle non-complex floats. I cleaned those up as part of this patch.
Wherever we checked for `is_float && !is_complex && !is_vector_type` i
just replaced it with the new API.

On encountering complex/vector floats, some of the ABI plugins would set
an error but then immediately overwrite the error to something else. I
just removed those branches entirely, since it was essentially dead
code.

Some of the diff is large because of un-indentation when we remove
if-guards, so I would recommend turning off white-space diff when
reviewing.