delay resolved procvar check for proc params + acknowledge unresolved statics (#23188)

fixes #23186

As explained in #23186, generics can transform `genericProc[int]` into a
call `` `[]`(genericProc, int) `` which causes a problem when
`genericProc` is resemmed, since it is not a resolved generic proc. `[]`
needs unresolved generic procs since `mArrGet` also handles explicit
generic instantiations, so delay the resolved generic proc check to
`semFinishOperands` which is intentionally not called for `mArrGet`.

The root issue for
[t6137](https://github.com/nim-lang/Nim/blob/devel/tests/generics/t6137.nim)
is also fixed (because this change breaks it otherwise), the compiler
doesn't consider the possibility that an assigned generic param can be
an unresolved static value (note the line `if t.kind == tyStatic: s.ast
= t.n` below the change in sigmatch), now it properly errors that it
couldn't instantiate it as it would for a type param. ~~The change in
semtypinst is just for symmetry with the code above it which also gives
a `cannot instantiate` error, it may or may not be necessary/correct.~~
Now removed, I don't think it was correct.

Still possible that this has unintended consequences.

(cherry picked from commit e8092a5470)

tests/misc/t8545.nim

@@ -1,5 +1,6 @@
 discard """
-  targets: "c cpp js"
+  # just tests that this doesn't crash the compiler
+  errormsg: "cannot instantiate: 'a:type'"
 """
 
 # bug #8545