Update tree_sitter for the new self syntax and static var (#7025)

This implements p7016 for tree_sitter. It also updates the build and
source file to allow this to build successfully and documents how to
successfully run these tests with Bazel given that it is fundamentally
not hermetic.

Assisted-by: Antigravity with Gemini

utils/tree_sitter/testdata/string/self_parameter.carbon

@@ -0,0 +1,11 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+class Point {
+  var x: i32;
+
+  fn GetX(self: Point) -> i32 { return self.x; }
+  fn GetY(self) -> i32 { return 0; }
+  fn SetX(ref self, new_x: i32) {}
+}

utils/tree_sitter/testdata/string/static_var.carbon

@@ -0,0 +1,7 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+class Widget {
+  static var count: i32;
+}