Rollup merge of #141876 - compiler-errors:missing-let-ty, r=SparrowLii

Don't declare variables in `ExprKind::Let` in invalid positions

Handle `let` expressions in invalid positions specially during resolve in order to avoid making destructuring-assignment expressions that reference (invalid) variables that have not yet been delcared yet.

See further explanation in test and comment in the source.

Fixes rust-lang/rust#141844

Author: matthiaskrgr