Back out r54608 (inline string literals were getting an extra '\0')

  temporarily, I assumed GetAddrForConstantString literal was being
  used consistently but it doesn't look like it is.

Factored out a CodeGenModule::getStringForStringLiteral which handles
  extracting a std::string for the bytes of a StringLiteral, padded to
  match the type.

Update EmitLValue to use getStringForStringLiteral, this was
  previously not padding strings correctly. Good thing we only emit
  strings in 4 different places!

llvm-svn: 54621