parser: port destructure, infix, pointer/slice attribute tests

Port tests:
- "destructure" (implement assign_destructure in
  expectVarDeclExprStatement)
- "infix operators" (partial — orelse as discard target deferred)
- "pointer attributes" (fix ** to parse inner modifiers per upstream)
- "slice attributes" (fix sentinel+align to use ptr_type node)

Fix test bodies to match upstream verbatim:
- "block with same line comment after end brace"
- "comments before var decl in struct"
- "comments before global variables"
- "comments in statements"
- "comments before test decl"

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

parser_test.zig

@@ -2882,6 +2882,57 @@ test "zig fmt: test declaration" {
     );
 }
 
+test "zig fmt: destructure" {
+    try testCanonical(
+        \\comptime {
+        \\    var w: u8, var x: u8 = .{ 1, 2 };
+        \\    w, var y: u8 = .{ 3, 4 };
+        \\    var z: u8, x = .{ 5, 6 };
+        \\    y, z = .{ 7, 8 };
+        \\}
+        \\
+        \\comptime {
+        \\    comptime var w, var x = .{ 1, 2 };
+        \\    comptime w, var y = .{ 3, 4 };
+        \\    comptime var z, x = .{ 5, 6 };
+        \\    comptime y, z = .{ 7, 8 };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: infix operators" {
+    try testCanonical(
+        \\test {
+        \\    var i = undefined;
+        \\    i = 2;
+        \\    i *= 2;
+        \\    i |= 2;
+        \\    i ^= 2;
+        \\    i <<= 2;
+        \\    i >>= 2;
+        \\    i &= 2;
+        \\    i *= 2;
+        \\    i *%= 2;
+        \\    i -= 2;
+        \\    i -%= 2;
+        \\    i += 2;
+        \\    i +%= 2;
+        \\    i /= 2;
+        \\    i %= 2;
+        \\    _ = i == i;
+        \\    _ = i != i;
+        \\    _ = i != i;
+        \\    _ = i.i;
+        \\    _ = i || i;
+        \\    _ = i!i;
+        \\    _ = i ** i;
+        \\    _ = i ++ i;
+        \\}
+        \\
+    );
+}
+
 test "zig fmt: precedence" {
     try testCanonical(
         \\test "precedence" {