Rollup merge of #144712 - nnethercote:dedup-num-types, r=fmease

Deduplicate `IntTy`/`UintTy`/`FloatTy`.

There are identical definitions in `rustc_type_ir` and `rustc_ast`. This commit removes them and places a single definition in `rustc_ast_ir`. This requires adding `rust_span` as a dependency of `rustc_ast_ir`, but means a bunch of silly conversion functions can be removed.

r? `@fmease`

Author: jdonszelmann