swift

fc9ea1e3 - Add Lexer::IsHashbangAllowed, drop SourceManager::getHashbangBufferID (#18534)

Add Lexer::IsHashbangAllowed, drop SourceManager::getHashbangBufferID (#18534) Having this be a single buffer hardcoded in the SourceManager and set by all clients is silly. SourceFiles with the 'Main' kind are allowed to have hashbang lines (`#!`), other files are not. And anyone manually setting up a Lexer can decide for themselves. No intended behavioral change.