[llvm] [MIR] Fix return value when computed properties conflict with given prop (PR #109923)

[Dominik Montada via llvm-commits]

gargaroff wrote:

Follow up to the failures coming from #108546. I realized that we returned `false` instead of `true`, leading the parser to believe that parsing was successful. With expensive checks enabled, this caused a crash coming from the newly added conflict test.

After using the correct return value, parsing is terminated gracefully with the error and the verifier doesn't crash anymore. This also required splitting up the conflict test as the other functions in the file wouldn't get parsed anymore.

Also noticed that `initializeCallSiteInfo` had the same issue, so changed the return value there as well.

https://github.com/llvm/llvm-project/pull/109923