macOS: switch to png for image

[Gae24]

Used png for handling images on all platform. On macOS dropped the dependency on core-graphics since now an image is directly stored as png

[complexspaces]

Hey there, thanks for the PR. Similar to the first PR which tried this, can I ask that you do some basic compatibility testing to make sure this doesn't regress any major use cases? Some examples would be:

• Copying image to and from Firefox, Chrome, and Safari
• Copying image to and from Pages and/or Word
• Copying image to and from TextEdit

[Gae24]

Unfortunately at the moment I don't have access to an Apple device.

[complexspaces]

I'm marking this one with both waiting on author and waiting on review since in theory either of us can perform the testing. No pressure here though, I'm just doing some status triage and cleanup.

[complexspaces]

I spent some time testing this today and my conclusion is that I believe we will need to continue to support TIFF on Apple platforms in order to retain compatibility with pasting images from Apple's own apps.

In my testing I used Chrome, Firefox, Screenshot tool, and a bunch of Electron apps. All of these had no issues with providing data in a PNG format. However when I tried pasting an image supplied by Pages.app, it failed. After some debug printing I saw that it only offers it in TIFF or HEIC (which image doesn't support).

I did try a different approach (getting a bitmap of RGBA from CGImage) that would support either PNG or TIFF more transparently but ran into another memory leak in Apple's image frameworks. When decoding TIFF data it leaks ~100 bytes, even inside of an autorelease pool. When decoding PNG there's no problems though. I guess it becomes a question of:

• How much do we care about consistency across platforms?
• How much do we want to drop the Rust tiff crate?
• Do people use TIFF enough in the "real world" via clipboard to run into the memory leaks?