[lldb/Core] Add SourceLocationSpec class (NFC)

A source location specifier class that holds a Declaration object containing
a FileSpec with line and column information. The column line is optional.
It also holds search flags that can be fetched by resolvers to look inlined
declarations and/or exact matches.

It describes a specific location in a source file and allows the user
to perform checks and comparaisons between multiple instances of that class.

Differential Revision: https://reviews.llvm.org/D100962



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>