improve compiler performance on dot fields after #24005

[metagn]

I noticed after #24005 the auto-reported boot time in PRs increased from around 8 seconds to 8.8 seconds, but I wasn't sure what could cause a performance problem that made the compiler itself compile slower, most of the changes were related to static which the compiler code doesn't use too often. So I figured it was unrelated.

However there is still a performance problem with the changes to tryReadingGenericParam. If an expression like a.b doesn't match any of the default dot field behavior (for example, is actually a call b(a)), the compiler does a final check to see if b is a generic parameter of a. Since #24005, if the type of a is not tyGenericInst or an old concept type, the compiler does a full traversal of the type of a to see if it contains a generic type, only then checking for c.inGenericContext > 0 to not return nil. This happens on every dot call.

Instead, we now check for c.inGenericContext > 0 first, only then checking if it contains a generic type, saving performance by virtue of c.inGenericContext > 0 being both cheap and less commonly true. The containsGenericType could also be swapped out for more generic type kind checks, but I think this is incorrect even if it might pass CI.

[github-actions]

Thanks for your hard work on this PR!
The lines below are statistics of the Nim compiler built from ebcfd96

Hint: mm: orc; opt: speed; options: -d:release
174154 lines; 8.231s; 655.215MiB peakmem