[clangd] Use name of Macro to compute its SymbolID, NFC.
We use the name from the IdentifierInfo of the Macro to compute its
SymbolID. It is better to just take the Name as a parameter to avoid
storing the IdentifierInfo whenever we need the SymbolID for the Macro.
Patch by UTKARSH SAXENA!
Reviewed By: hokein
Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, cfe-commits
Differential Revision: https://reviews.llvm.org/D69937