[SPARK-56054][SQL] Add test for MERGE INTO schema evolution with aliased assignments

[johanl-db]

What changes were proposed in this pull request?

Follow up from #54891 in particular this comment.

Adds more tests covering schema evolution in MERGE INTO when the assignment contains an alias.
This change also undoes the fix from #54891. On closer inspection, this isn't needed in Spark as Spark already removes trivial aliases on nested field accessors in MERGE in resolveExprInAssignment, which is what the change aimed to allow. See this test added here covering trivial aliases implictily added on nested field access.

Delta doesn't strip aliases during resolution in that way and will require special handling, but that's up to Delta to implement in its custom resolution logic to replicate what Spark already does

How was this patch tested?

Adds tests covering MERGE INTO schema evolution with aliases in assignments

[szehon-ho]

these are all DataFrame API, wondering is there any equivalent in SQL? Be good to abstract it out if possible

If not, maybe we can we make a new file MergeIntoSchemaEvolutionExtraDataFrameTests to make them only run in DataFrame mode?

It is a bit of a mess now due to the inheritance patterns

[johanl-db]

I moved the tests to a dedicated trait for dataframe tests.

There's no SQL equivalent, it's not possible to specify an alias in an assignment expression using SQL afaict: SET col = source.col AS other_col