[llvm] [clang] [mlir] [llvm][TypeSize] Fix addition/subtraction in TypeSize. (PR #72979)

[Paul Walker via cfe-commits]

paulwalker-arm wrote:

> The static functions renaming is going to produce a lot of noise but I guess this is too late already... Shall we revert to keep the change minimal? @nikic @paulwalker-arm WDYT ?

For my money the function's were originally named correctly and then erroneously changed to (a) diverge from the coding stand, and (b) unknowingly introduce a bug caused by the new naming.  For both reasons I'm happy to revert to the original naming via this patch.

https://github.com/llvm/llvm-project/pull/72979