menu: Use focus to determine OSK/textbox behavior

[Ryunam]

Description

Following the concerns raised in #19213, I have reworked the OSK/textbox behavior to retain compatibility with controller keyboards (such as the IPAC devices mentioned in that PR) while still preserving the improvements to text typing with physical keyboards.

This PR adds a new focus switching mechanism:

• When focus is on the OSK (which is always by default when selecting "Rename" for any playlist entry), behavior is restored to its "legacy" state: keyboard arrows move the cursor over OSK keys/buttons; both Left-CTRL and Right-CTRL act as confirmation/press. The CTRL keys respond to whether the user chose to swap the Confirm and Cancel RetroPad buttons, just like it was before.
• When focus is on the textbox, instead, the "new" behavior is applied: keyboard arrows move the caret over the typed text, while holding CTRL allows to move between space-delimited words.

Two ways are provided for switching the focus between OSK and textbox:

• Pressing the TAB keyboard key.
• If using a mouse, clicking with the pointer over the OSK and/or textbox areas will switch focus to one of the two, respectively.

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A few pictures of how the focus looks with the different menu drivers.

Ozone:

Focus on OSK (default)

Focus on textbox

MaterialUI / GLUI

Focus on OSK (default)

Focus on textbox

XMB

Focus on OSK (default)

Focus on textbox

RGUI

Focus on OSK (default)

Focus on textbox

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Reviewers

@sonninnos