reset inTypeofContext in generic instantiations

[metagn]

fixes #24228, refs #22022

As described in #24228 (comment), instantiating generic routines inside typeof causes all code inside to be treated as being in a typeof context, and thus preventing compile time proc folding, causing issues when code is generated for the instantiated routine. Now, instantiated generic procs are treated as never being inside a typeof context.

This is probably an arbitrary special case and more issues with the typeof behavior from #22022 are likely. Ideally this behavior would be removed but it's necessary to accomodate the current proc declval in the package stew, at least without changes to compileTime that would either break other code (making it not eagerly fold by default) or still require a change in stew (adding an option to disable the eager folding).

Alternatively we could also make the eager folding opt-in only for generic compileTime procs so that #22022 breaks nothing whatsoever, but a universal solution would be better. Edit: Done in #24230 via experimental switch

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