Avoid broken kind type handling when compiling `isa` (#27736)
* small workaround checks against incorrect subtyping for kind types for isa_tfunc
* add test for #27078
* fix pretty crazy bug where Type{T}s were inferred as Ts
* work around broken subtyping in emit_isa codegen optimization
* a test that was checking for exact/optimal inference result is now broken
Justification for allowing this test to remain broken for now:
- benchmarking the expression (including downstream toy calculations on the output, e.g. broadcast sin) using BenchmarkTools reveals no actual performance difference
- inference returning an optimal result before was probably reliant on the broken subtyping behavior; correctness >>> performance
- inference is still returning a fairly tightly bounded, correct Union type
