Add an option for stylus users to have hotkeys available while holding the mouse button

[misaki-eymard]

In v4.0.43, an update was made to make hotkeys unavailable while the mouse button is pressed, which some have said is inconvenient for stylus users.
For example, it used to be possible to drag the timeline bar in the Dopesheet view with the stylus and then press the D hotkey while holding down the stylus to stop the animation. When using a mouse, it is easy to fix the cursor at a certain position, so even if you have to press a hotkey after releasing the mouse button once, you can easily adjust the timeline bar to the same frame by immediately clicking again, but it is hard to fix the cursor at the same frame using the stylus, so there is a need to use hotkeys while holding something in place by dragging. We could consider an option for stylus users to allow hotkeys even when the mouse button is pressed.

Related thread: https://esotericsoftware.com/forum/d/26798-40-clicks-dont-stop-during-playback

[NathanSweet]

Disallowing hotkeys while the mouse/stylus is pressed prevents bugs throughout the app. Sometimes a hotkey can disrupt the functionality from pressing or clicking the mouse, resulting in rare state that is difficult to protect against. Given that, we probably don't want to enable it for the whole app like it used to be.

We could allow hotkeys depending on the mouse drag behavior. For example, dragging the timeline could still allow hotkeys with likely few unexpected side effects.