[CP] Fix crash on choosing share in selection controls on ipad

[LouiseHsu]

Fixes flutter/flutter#138550

Original PR: #48220

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide] and the [C++, Objective-C, Java style guides].
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or the PR is [test-exempt]. See [testing the engine] for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the [CLA].
• All existing and new tests are passing.

[LinXunFeng]

Suggested change

	std::unique_ptr<fml::WeakNSObjectFactory<FlutterEngine>> _weakFactory =
	std::make_unique<fml::WeakNSObjectFactory<FlutterEngine>>(engine);
	std::unique_ptr<fml::WeakPtrFactory<FlutterEngine>> _weakFactory =
	std::make_unique<fml::WeakPtrFactory<FlutterEngine>>(engine);

We need to temporarily change back to the old type to pass checks.

[LinXunFeng]

Suggested change

	[[FlutterPlatformPlugin alloc] initWithEngine:_weakFactory->GetWeakNSObject()];
	[[[FlutterPlatformPlugin alloc] initWithEngine:_weakFactory->GetWeakPtr()] autorelease];

Here too.

[jmagman]

@CaseyHillers this and flutter/flutter#139102 is approved. Do you merge or should @LouiseHsu?