Support package:web ^0.5.0

[navaronbracke]

This PR updates google_maps to support the new release of package:web

• update package:web/helpers.dart import to package:web/web.dart
• document.querySelector() instead of the deprecated querySelector()
• since package:web no longer exports bindings for non-standard API's, I've opted to patch it with an extension type, which required a bump to Dart 3.3.

See https://github.com/dart-lang/web/blob/main/CHANGELOG.md#050

Currently, the API needs to be standards-track, and be supported by Safari, Chrome, and Firefox.

Context: https://github.com/flutter/packages/pull/5254#discussion_r1495188143

[kevmoo]

Need a changelog, too?

[navaronbracke]

Need a changelog, too?

Ah, right. I'll add one entry.

[a14n]

Thanks!

[a14n]

7.1.0 is now published