Mica support on Win32 platform

[Luminoso-256]

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Adds support for a window to utilize darkmode and Windows 11-style taskbars by defining SA_Win11 before inclusion of Slimapp. Requires that the app links to dwmapi.lib

Note that the changes require Windows 11 Insider Preview 22523 or higher to work for Mica. Before 22523, the only easy way to set Mica was through an undocumented attribute.

Not entirely sure if this is in scope, but was fun to add and figured I might as well PR it in case. Cheers!

[HardCoreCodin]

Hey, thanks for the contribution :) Generally, I would want to avoid any additional specific dependencies, or operating system version requirements, as the whole point of the 'Slim' in the name there is to minimize dependencies and setup effort. Though, as long as it's all technically 'optional' and doesn't impose any additional requirement (code would still compile in much older version of Window), then I don't mind accepting it.

[Luminoso-256]

The code should still compile in older windows versions just fine. Anything added in my PR is wrapped in an #ifdef SA_Win11 block, so without that definition it imposes no extra requirements.