Cache delegate for non-capturing local functions when caching delegates for static methods

[pawchen]

This issue is created in respond to #6642 (comment)

Currently #6642 avoids local functions completely, as local functions all appears IsStatic but they could capture things. When it makes into a feature branch, consider support them like non-capturing lambda.

Also need to consider what to do when the delegate type involves generic parameters from any local functions.

[jcouv]

FYI @agocke (relates to local functions)

[pawchen]

Closing as this is done in #58288. Just mark the targeting local function as static.