feat: add accept_first_mouse for macOS

[z4122]

• Tested on all platforms changed
• Compilation warnings were addressed
• cargo fmt has been run on this branch
• cargo doc builds successfully
• Added an entry to CHANGELOG.md if knowledge of this change could be valuable to users
• Updated documentation to reflect any user-facing changes, including notes of platform-specific behavior
• Created or updated an example program if it would help users understand this functionality
• Updated feature matrix, if new features were added or implemented

On macOS, change the default behavior for first click when window was unfocused. Now window will become focused and then respond to the click event when mouse clicks.
To keep consistent with windows.

[ArturKovacs]

Hi there! Welcome to winit and thanks for the contribution. 😊

It's looking good.

[ArturKovacs]

@murarth if you take a look and this and approve it, then I'll be able to merge it. It works as expected so at this point just general code quality check is enough I believe.

[ArturKovacs]

@z4122 if you fix the conflicts, I'll merge this without waiting for other maintainers.

[madsmtm]

This looks good to me, it matches what I would expect from a winit application!

At some point we should consider making it user-configurable, but let's wait until someone comes with a concrete use-case!

[ArturKovacs]

I rebased onto the master, and force-pushed the changes.

[ArturKovacs]

It's somewhat annoying that the "nightly-x86_64-pc-windows-gnu" target fails spuriously :/