Use objc2

[madsmtm]

I suspect it'll take a while before winit will be in a state where tao can use that directly, so in the meantime, let's slowly start transitioning tao to objc2. I tried to make this transition in a way that minimizes the amount of code changes, but it's really hard to separate things out, so it ended up being quite large anyways.

Full disclosure: The biggest reason why I'm doing this is to reduce the number of dependencies on objc across the ecosystem, I don't intend on fully finishing the transition in tao / making full use of the features offered by objc2 (hopefully winit will be ready to be usable for you one day).
But I think even this initial transition can be valuable to you, as it fixes at least some of the memory leaks currently present, and makes it easier to develop new features (including visionOS support).

I've tested every example on macOS 14.7.1, and on Mac Catalyst (works very poorly here, but at least we don't trigger any obvious encoding validation errors).

Builds upon #1048.
Fixes the last part of tauri-apps/wry#1239.

CC @pewsheen since you did the work in wry.

[madsmtm]

Though I guess rejecting this PR would push me towards working more on getting Winit into a state where tao can use it as a dependency... ;)

[github-actions]

Package Changes Through e9008dd

There are 1 changes which include tao with minor

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
tao	0.31.1	0.32.0

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[amrbashir]

Though I guess rejecting this PR would push me towards working more on getting Winit into a state where tao can use it as a dependency... ;)

No way, objc2 is awesome and I would accept this PR asap but I don't have macOS test, @pewsheen @FabianLars can any of you test and review this PR?

[amrbashir]

oops..

[amrbashir]

ofc the ultimate goal is to go back to winit as a dependency. I was thinking about creating a crate that uses git submodule to generate a glue code that re-exports winit on macOS and Windows, and delegates onto gtk on Linux, although I think a Platfrom trait that could be implemented externally could be the better way to go.