When TAStudio is focused, keybinds that include Alt don't work

[YoshiRulz]

The default keybind for "Delete Branch" is Alt+Delete, causing some confusion.

Cause appears to be this:

BizHawk/src/BizHawk.Client.EmuHawk/Input/Input.cs

Lines 254 to 260 in 44bf67e

	AllowInput allowInput = MainFormInputAllowedCallback(false);
	foreach (var ie in _newEvents)
	{
	//events are swallowed in some cases:
	if ((ie.LogicalButton.Modifiers & LogicalButton.MASK_ALT) is not 0U && ShouldSwallow(MainFormInputAllowedCallback(true), ie))
	continue;

BizHawk/src/BizHawk.Client.EmuHawk/MainForm.cs

Lines 528 to 535 in 44bf67e

	yieldAlt => ActiveForm switch
	{
	null => Config.AcceptBackgroundInput // none of our forms are focused, check the background input config
	? Config.AcceptBackgroundInputControllerOnly
	? AllowInput.OnlyController
	: AllowInput.All
	: AllowInput.None,
	TAStudio when yieldAlt => AllowInput.None,

[SuuperW]

Coming from my duplicate issue.

This is intentional from what I see, present for a long long time.

This is really more an issue due to the fact we have various default hotkeys for TAStudio which use Alt.

Okay, a commit almost 10 years ago that says nothing about why this is for TAStudio specifically. Likely the reason for singling out TAStudio is that it's the only tool where this matters. All others except Virtual Pad disallow hotkeys when focused and Virtual Pad blocks the normal menu function of Alt.
There's also f8f1906, MainForm has special code to make Alt hotkeys work.

I see no reason to have this behavior difference between TAStudio and the MainForm (or Virtual Pad, but I never used that). Perhaps FormBase should implement the special alt handling logic, rather than MainForm.