Fix symbol table patching for overriding default methods

[Trundle]

ast_replace (potentially) copies the input AST, hence it's important
to do the symbol table patching on the output AST. Otherwise the
patching will happen on the wrong nodes, which leads to methods with
a wrong symbol table.

Fixes #3305

[ponylang-main]

Hi @Trundle,

The changelog - fixed label was added to this pull request; all PRs with a changelog label need to have release notes included as part of the PR. If you haven't added release notes already, please do.

Release notes are added by creating a uniquely named file in the .release-notes directory. We suggest you call the file 3719.md to match the number of this pull request.

The basic format of the release notes (using markdown) should be:

## Title

End user description of changes, why it's important,
problems it solves etc.

If a breaking change, make sure to include 1 or more
examples what code would look like prior to this change
and how to update it to work after this change.

Thanks.

[SeanTAllen]

The test here is different than @EpicEric's minimal example from #3305, however, I verified that this change fixes #3305.

[SeanTAllen]

This is an awesome first contribution @Trundle. Thanks.

Can you add release notes? If that is done before Friday, this can go out with the release that is happening on Friday.

[Trundle]

Whoops I should have probably mentioned this, yes. The other tests mostly use traits and not interfaces. As the bug happens with both, I tried to be consistent with the other tests.

I added some release notes, I hope that's how it works. I unfortunately forgot to add a "ci skip" though :/

[SeanTAllen]

@Trundle no need to worry about skip ci

[SeanTAllen]

@Trundle release notes look good. This will go out with tomorrow's release. Thanks!