parser: add struct/array literal tests (2/3 element variants)

Port tests from upstream parser_test.zig:
- "struct literal 2/3 element" (with and without comma)
- "anon list literal 1/2/3 element" (with and without comma)
- "array literal 0/1/2/3 element" (with and without comma)

All 17 new tests pass without parser changes — the init list
implementation from the previous commit handles all cases.

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

parser_test.zig

@@ -1026,3 +1026,183 @@ test "zig fmt: struct literal 1 element" {
         \\
     );
 }
+
+test "zig fmt: struct literal 2 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = X{ .a = b, .c = d };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: struct literal 2 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = X{
+        \\        .a = b,
+        \\        .c = d,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: struct literal 3 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = X{ .a = b, .c = d, .e = f };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: struct literal 3 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = X{
+        \\        .a = b,
+        \\        .c = d,
+        \\        .e = f,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 1 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{a};
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 1 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{
+        \\        a,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 2 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{ a, b };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 2 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{
+        \\        a,
+        \\        b,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 3 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{ a, b, c };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: anon list literal 3 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = .{
+        \\        a,
+        \\        // foo
+        \\        b,
+        \\
+        \\        c,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 0 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = [_]u32{};
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 1 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = [_]u32{a};
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 1 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = [1]u32{
+        \\        a,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 2 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = [_]u32{ a, b };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 2 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = [2]u32{
+        \\        a,
+        \\        b,
+        \\    };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 3 element" {
+    try testCanonical(
+        \\test {
+        \\    const x = [_]u32{ a, b, c };
+        \\}
+        \\
+    );
+}
+
+test "zig fmt: array literal 3 element comma" {
+    try testCanonical(
+        \\test {
+        \\    const x = [3]u32{
+        \\        a,
+        \\        b,
+        \\        c,
+        \\    };
+        \\}
+        \\
+    );
+}