[SYCL][Libclc] Alter libclc-remangler to use clang mangling

[AidanBeltonS]

Is your feature request related to a problem? Please describe
Currently, the libclc-remangler manually mangles builtins. Manual mangling has two issues. The first is that it leads to code duplication, where both clang and the remangler have different methods to perform the same task.
The second is that it leads to more bugs and maintenance work. For example, if the clang mangler deviates from the expected mangling behaviour, this creates bugs. Additionally, if the clang mangler gets updated, the remangler may need to be patched to behave the same.

Describe the solution you would like
The solution would be to adjust the remangler to use clang's mangling tools. Using clang's mangling tools would mitigate the previously stated issues as there would be only one area of code responsible for built-in mangling. It would also keep the remangler consistent with any upstream llvm changes.

Describe alternatives you have considered
The other alternative is to maintain and manage the libclc-remangler constantly.

Additional context
This issue partly relates to: #5849