Binding pattern naming cleanup (#3410)

- Rename `PatternBinding` to `BindingPattern`.
- Use `BindingPattern` rather than `Pattern` in the names of
binding-pattern-specific parse states.

toolchain/check/node_stack.cpp

@@ -14,7 +14,7 @@ auto NodeStack::PrintForStackDump(llvm::raw_ostream& output) const -> void {
   for (auto [i, entry] : llvm::enumerate(stack_)) {
     auto parse_node_kind = parse_tree_->node_kind(entry.parse_node);
     output << "\t" << i << ".\t" << parse_node_kind;
-    if (parse_node_kind == Parse::NodeKind::PatternBinding) {
+    if (parse_node_kind == Parse::NodeKind::BindingPattern) {
       output << " -> " << entry.name_id;
     } else {
       if (entry.inst_id.is_valid()) {