Auto merge of #67707 - petrochenkov:crateren, r=Centril

Auto merge of #67707 - petrochenkov:crateren, r=Centril

Rename some crates and modules in the frontend

Migrate from `syntax_*` naming scheme to `rustc_*`.
See https://github.com/rust-lang/rust/pull/65324#issuecomment-551103396 and several comments below.

Renamed crates:
`syntax_expand` -> `rustc_expand`
`syntax_pos` -> `rustc_span` ([motivation](https://github.com/rust-lang/rust/pull/65324#issuecomment-552173320))
`syntax_ext` -> `rustc_builtin_macros`

Also one module in resolve is renamed for consistency and to avoid tautology.

r? @Centril