Rollup merge of #123993 - compiler-errors:coroutine-obl, r=lcnr

Do `check_coroutine_obligations` once per typeck root

We only need to do `check_coroutine_obligations` once per typeck root, especially since the new solver can't really (easily) associate which obligations correspond to which coroutines.

This requires us to move the checks for sized coroutine fields into `mir_coroutine_witnesses`, but that's fine imo.

r? lcnr

compiler/rustc_span/src/source_map.rs

@@ -14,7 +14,7 @@ use rustc_data_structures::sync::{IntoDynSyncSend, MappedReadGuard, ReadGuard, R
 use rustc_data_structures::unhash::UnhashMap;
 use std::fs;
 use std::io::{self, BorrowedBuf, Read};
-use std::path::{self};
+use std::path;
 
 #[cfg(test)]
 mod tests;