Quick-focus keyboard shortcuts, inconsistencies in landing spots depending on docked vs. centred modal modes

[danielweck]

Follow-up to https://github.com/edrlab/thorium-reader/commit/4f0a1ba0305b2d5a864c55a64bed3c778cda88cf

See: https://github.com/edrlab/thorium-reader/issues/2322#issuecomment-2133805270

The focus landing in the centred modal dialog is not the selector tab GUI control of "table of contents" or "goto page" (unlike in docked panel), it is the "left-docking" icon (or the "custom text format" checkbox in the case of invoking the settings shortcut). This inconsistency should be fixed, if technically possible.