language: add module name field to @src

closes #20963

test/behavior/src.zig

@@ -7,11 +7,13 @@ fn doTheTest() !void {
     try expect(std.mem.endsWith(u8, src.file, "src.zig"));
     try expect(src.fn_name[src.fn_name.len] == 0);
     try expect(src.file[src.file.len] == 0);
+    if (!std.mem.eql(u8, src.module, "test") and !std.mem.eql(u8, src.module, "root")) return error.TestFailure;
 }
 
 const std = @import("std");
 const builtin = @import("builtin");
 const expect = std.testing.expect;
+const expectEqualStrings = std.testing.expectEqualStrings;
 
 test "@src" {
     if (builtin.zig_backend == .stage2_aarch64) return error.SkipZigTest; // TODO