Reverts "[ios][platform_view] Use CAShapeLayer as the mask to avoid software rendering (#53072)"

[auto-submit]

Reverts: #53072

Initiated by: jason-simmons

Reason for reverting: compilation errors on iOS targets

FlutterPlatformViews_Internal.mm:277:10: error: ARC forbids explicit message send of 'dealloc'
  277 |   [super dealloc];
      |    ~~~~~ ^

(see https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8746006425774972161/+/u/build_ci_ios_debug_unopt_sim_flutter_testing_scenario_app_flutter_shell_platform_darwin_ios:ios_test_flutter/st

Original PR Author: hellohuanlin

Reviewed By: {cbracken, jonahwilliams}

This change reverts the following previous change:
This PR uses CAShapeLayer as the mask to avoid software rendering.

I kept UIView as the mask, so that we can measure just the improvement related to avoiding software rendering. This also allows me to land this change sooner. I created a separate issue to track removing UIView as the mask.

Note: the previous behavior seems to be incorrect (or at least not pixel perfect). This PR fixed it. See comments.

See design doc: https://docs.google.com/document/d/1TqG_N4GK_qctuk73Gk3zOdAiILUrwMqxoCMgroK_AeA/edit?resourcekey=0-jUiidfzIS642ngG2w9vSUA&tab=t.0

List which issues are fixed by this PR. You must list at least one issue.

Fixes flutter/flutter#142813
Fixes flutter/flutter#142830

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