Deprecate these old APIs

Remove 1745 decorative breaks

SelectionChangedCause for iOS keyboard-select

Add support for iOS UndoManager

This reverts commit 3cde69e8.

Relands the "Scribble mixin" PR, which was reverted due to breaking a Google test in the last roll.
Breaks the Scribble feature out of TextInputClient in order to avoid breaking changes.

This reverts commit b571abfb.

Refactors methods related to the iPad Scribble feature out of TextInputClient

This reverts commit c54ce015.

This adds avoid_dynamic_calls to the list of lints, and fixes all instances where it was violated.

Importantly, this lint is NOT turned on for flutter/packages/test, because those changes are happening in another PR: #84478

This reverts commit 35ad43f2.

This reverts commit 285b4751.

This reverts commit c26ed03c.

* Migrate to ChannelBuffers.push

* Move TestDefaultBinaryMessenger to its own file

* Apply deprecations and fix usages

This reverts commit b070ed3c.

This reverts commit 67d8556b.

This reverts commit 5e4e530e.