Respect "-fdiagnostics-absolute-paths" on emit include location

This commit fixes "TextDiagnostic::emitIncludeLocation" when compiling
with "-fdiagnostics-absolute-paths" flag enabled by emitting the absolute
path of the included file.

Fixes #63026

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D151833