IBC fixes (dotnet/coreclr#26738)

IBC fixes (dotnet/coreclr#26738)

* IBC fixes
- Support IntPtr and UIntPtr element types in IBC data
- More defensive coding against structurally incorrect IBC data
- Skip compilation of open method definitions
- Generate IBC data without crashing when the first logged item is an InstantiatedMethod and not a token
- Safely shutdown and emit IBC data from a thread that hasn't been given a Thread object

Commit migrated from https://github.com/dotnet/coreclr/commit/d31557c467fb4eb3fa66481c3a81e63fb2c8eb94