Adaptions are for this gocui commit:
Cleanup: remove Is* error functions
- Use errors.Is instead of quality comparisons. This is better because it
matches wrapped errors as well, which we will need later in this branch.
- Inline the errors.Is calls at the call sites. This is idiomatic go, we don't
need helper functions for this.
See https://go.dev/blog/go1.13-errors for more about this.
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