[material_ui] Migrate M3 IconButton template to use new gen_defaults

[QuncCccccc]

Work toward flutter/flutter#187899.
Fixes flutter/flutter#188417.

This PR migrates the M3 IconButton defaults templates to use the new gen_defaults in material_ui.

The IconButton, FilledIconButton, FilledTonalIconButton, and OutlinedIconButton defaults are generated into separate files. The generated defaults remain unchanged.

Pre-Review Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [AI contribution guidelines] and understand my responsibilities, or I am not using AI tools.
• I read the [Tree Hygiene] page, which explains my responsibilities.
• I read and followed the [relevant style guides] and ran [the auto-formatter].
• I signed the [CLA].
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I [linked to at least one issue that this PR fixes] in the description above.
• I followed [the version and CHANGELOG instructions], using [semantic versioning] and the [repository CHANGELOG style], or I have commented below to indicate which documented exception this PR falls under[^1].
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which [test exemption] this PR falls under[^1].
• All existing and new tests are passing.