Rollup merge of #73597 - ayazhafiz:i/const-span, r=ecstatic-morse

Record span of `const` kw in GenericParamKind

Context: this is needed for a fix of https://github.com/rust-lang/rustfmt/issues/4263,
which currently records the span of a const generic param incorrectly
because the location of the `const` kw is not known.

I am not sure how to add tests for this; any guidance in how to do so
would be appreciated :slightly_smiling_face:

diff --cc src/librustc_ast/ast.rs
Simple merge

diff --cc src/librustc_ast/mut_visit.rs
Simple merge

diff --cc src/librustc_ast_lowering/lib.rs
Simple merge

diff --cc src/librustc_ast_pretty/pprust.rs
Simple merge

diff --cc src/librustc_resolve/late.rs
Simple merge