Rollup merge of rust-lang#77932 - ssomers:btree_cleanup_gdb, r=Mark-Simulacrum

BTreeMap: improve gdb introspection of BTreeMap with ZST keys or values

I accidentally pushed an earlier revision in rust-lang#77788: it changes the index of tuples for BTreeSet from ""[{}]".format(i) to "key{}".format(i). Which doesn't seem to make the slightest difference on my linux box nor on CI. In fact, gdb doesn't make any distinction between "key{}" and "val{}" for a BTreeMap either, leading to confusing output if you test more. But easy to improve.

r? @Mark-Simulacrum

Author: Dylan-DPC

alloc/src/collections/btree/node.rs

@@ -87,7 +87,6 @@ impl<K, V> LeafNode<K, V> {
 #[repr(C)]
 // gdb_providers.py uses this type name for introspection.
 struct InternalNode<K, V> {
-    // gdb_providers.py uses this field name for introspection.
     data: LeafNode<K, V>,
 
     /// The pointers to the children of this node. `len + 1` of these are considered