Rollup merge of #136149 - cuviper:rustc-rayon-indexmap, r=compiler-errors

Flip the `rustc-rayon`/`indexmap` dependency order

[`rustc-rayon v0.5.1`](rust-lang/rustc-rayon#14) added `indexmap` implementations that will allow `indexmap` to drop its own "internal-only" implementations.

(This is separate from `indexmap`'s implementation for normal `rayon`.)

Author: matthiaskrgr