Auto merge of #134478 - compiler-errors:attr-span, r=oli-obk

Properly record metavar spans for other expansions other than TT

This properly records metavar spans for nonterminals other than tokentree. This means that we operations like `span.to(other_span)` work correctly for macros. As you can see, other diagnostics involving metavars have improved as a result.

Fixes #132908
Alternative to #133270

cc `@ehuss`
cc `@petrochenkov`

Author: bors