Rollup merge of #149329 - Jarcho:for_question_ctxt, r=davidtwco

Mark match arms in try and for as being from desugarings.

Some of the arms created by these desugarings have an expression which isn't marked as coming from the desugaring. e.g. try generates `Continue(val) => val` where the expression has the span of the original parameter (done for diagnostic purposes). Since the arm created just used that span they end up without a desugaring mark unnecessarily.

This is only a minor annoyance with some work I'm doing in clippy.

Author: JonathanBrouwer