sem: make isCyclical work with resolved concepts

[zerbina]

Summary

Make the isCyclical type-trait return whether the bound type for
resolved concept types is cyclical, instead of always false.

Details

• change the "is concrete" test in evalTypeTrait to "skip" resolved
  concept types
• consider all resolved concept types in types.productReachable (used
  in implementing the isCyclical type trait), not just generic
  concept types
• extend the tcyclic.nim test with a test case for resolved concept
  operands

[zerbina]

This change fixes the bug causing a CI failure #1646. The relevant part is the change to productReachable -- the fix for isCyclical is just included so that the productReachable fix can be tested (productReachable is transitively called by the isCyclical implementation).

[zerbina]

/merge

[github-actions]

Merge requested by: @zerbina

Contents after the first section break of the PR description has been removed and preserved below:

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Notes for Reviewers

• partially split out from implement a new CGIR and C code generator #1625