* Convert Special / Global function page to flex layout.
Move function name text into row button so entire row acts as a button.
Display active functions first, then inactive functions as smaller buttons in a grid.
* Merge duplicate cases in switch, fix indentation.
* Keep selected button focussed after editing a function.
Add long press handler to jump between free and used functions.
* Revert to numerical order for functions list.
Use context menu for empty functions all the time.
* Fix parameter type and remove redundant lines.
* Fix incorrect function being selected when changing tabs.
* Fix selection of focussed button when using 'Clear', 'Delete' and switching tabs.
* Change button style to match input/mixes/outputs pages.
* Fix checked state display for buttons.
* Fix scroll position when adding new entries at the bottom. Center selected button after editing or changes to list.
* Remove logic that tries to center scroll around selected button (not working).
* Convert overview button to lvgl grid.
Display function as more readable expression instead of discrete values.
Single line display for overview button on landscape screen.
Fix display when editing GVAR INC/DEC value (was '--' instead of '-=').
Fix incorrect module displayed for 'Set Failsafe' (swapped).
Show all parameter and values for each function type in overview.
* Fix 'Enabled' indicator so it is not selectable with the scroll wheel and looks less like a radio button.
* Remove empty buttons and add a single '+' button at the bottom to match inputs and mixes.
* Add long press handler for quick access to the '+' button functions.
* Ensure addButton is initialised if not needed (list is full).
* Use formatNumberAsString helper function.
* Adjust grid spacing.
* fix: `STR_VALUE` not `STR_VOLUME`
