[material_ui] Standardize M3 and M3E token template base class names

[elliette]

Work towards flutter/flutter#191088

Ports over #12209 which landed on the m3e_migration feature branch.

Original PR description

As title. Related to flutter/flutter#187899

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[gemini-code-assist]

Code Review

This pull request renames the template classes M3TokenTemplate and M3ETokenTemplate to TokenTemplateM3 and TokenTemplateM3E, and updates the generated file naming convention from *_m3_defaults.g.dart to *_defaults_m3.g.dart. The corresponding tests and test fixtures have been updated to reflect these changes. Feedback is provided regarding a missing blank line between test blocks in the test suite to maintain consistency and readability.

[gemini-code-assist]

For better readability and consistency with the rest of the test suite, please maintain a blank line between the test blocks.

Suggested change

	});
	test('will run dart format over the generated file', () {
	});
	test('will run dart format over the generated file', () {