When QuickJit is enabled, disable it for methods that contain loops by default (dotne...

When QuickJit is enabled, disable it for methods that contain loops by default (dotnet/coreclr#24252)

When QuickJit is enabled, disable it for methods that contain loops by default

Fixes https://github.com/dotnet/coreclr/issues/19751 by default when QuickJit is enabled
- Added config variable TC_QuickJitForLoops. When disabled (the default), the JIT identifies loops and explicit tail calls and switches to tier 1 JIT.
- This would prevent the possibility of spending too long in QuickJit code, but may decrease startup time a bit when QuickJit is enabled
- Removed TC_StartupTier_OptimizeCode, as now that there is TC_QuickJit, I didn't see a good use for it
- Removed references to "StartupTier" in config variables because we had previously decided not to call it that.
- When QuickJit is disabled, avoid creating native code slots for methods in non-R2R'ed modules, as tiering would be disabled for those anyway
- Marked TC_QuickJit config var as external

Commit migrated from https://github.com/dotnet/coreclr/commit/607c8db3931cc4f4afe086f2cd4dd957d35ef0ac