Rename and reorder lots of lifetimes.

- Replace non-standard names like 's, 'p, 'rg, 'ck, 'parent, 'this, and
  'me with vanilla 'a. These are cases where the original name isn't
  really any more informative than 'a.
- Replace names like 'cx, 'mir, and 'body with vanilla 'a when the lifetime
  applies to multiple fields and so the original lifetime name isn't
  really accurate.
- Put 'tcx last in lifetime lists, and 'a before 'b.

compiler/rustc_mir_transform/src/deduplicate_blocks.rs

@@ -98,7 +98,7 @@ fn find_duplicates(body: &Body<'_>) -> FxHashMap<BasicBlock, BasicBlock> {
     duplicates
 }
 
-struct BasicBlockHashable<'tcx, 'a> {
+struct BasicBlockHashable<'a, 'tcx> {
     basic_block_data: &'a BasicBlockData<'tcx>,
 }