Add Expr::try_as_col, deprecate Expr::try_into_col (speed up optimizer)

[alamb]

Which issue does this PR close?

Part of #9637

I ran into this while working on #10444

Rationale for this change

There are places in the code that check if an expr is a column by using Expr::try_into_col() which has two potential performance problems:

1. It requires cloning the Column (and thus a string) to check if an expr is a Expr::Column
2. It requires creating and ignoring a DataFusionError to check if an expr is not a Expr::Column

What changes are included in this PR?

1. Add Expr::try_as_col
2. Deprecate Expr::try_into_col
3. Change code to use Expr::try_into_col

Are these changes tested?

By existing tests

Are there any user-facing changes?

A new function / less required copying

I doubt we will see any significant performance changes however it does reduce allocations during planning

[alamb]

Thanks @sadboy 🙏

[tustvold]

Most places seem to still be cloning it, but I guess baby steps 😅

[alamb]

Most places seem to still be cloning it, but I guess baby steps 😅

Yes indeed -- baby steps. Thank you for the review @tustvold

Another thing that would likely help non trivially would be to introduce a version of Expr::to_columns that does not requiring cloneing each Column. I'll file at ticket about that too

[alamb]

I think making the error here (rather than in try_into_col) results in a more specific error message that will be easier to debug if we ever hit it