feat: keybind hint overlay

[NathanFlurry]

What does this PR do?

Fixes #8730

Added settings:

• keybind_hint.enabled (default true)
• keybind_hint.delay_ms

How did you verify your code works?

Manually tested, both from home screen and from session with different screen sizes.

Screenshots

In-session

Home screen

Tiny screen

Large screen