Optimize the codegen for Span::from_expansion

[Jarcho]

See https://godbolt.org/z/bq65Y6bc4 for the difference. the new version is less than half the number of instructions.

Also tried fully writing the function by hand:

sp.ctxt_or_parent_or_marker != 0
        && (
            sp.len_with_tag_or_marker == BASE_LEN_INTERNED_MARKER 
            || sp.len_with_tag_or_marker & PARENT_TAG == 0
        )

But that was no better than this PR's current use of match_span_kind.

[rustbot]

r? @jieyouxu

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[Urgau]

Is this function this hot that it needs micro-optimized? Have you benchmark it on real world case?

[Jarcho]

There are more than 300 call sites (most from clippy) and it ends up being called more than once per expression while linting (in clippy). It's definitely used a lot and frequently called.

[jieyouxu]

r? @petrochenkov