Nav: added io.ConfigNavEscapeClearFocusItem. (#8059, #2048, #1074, #3200)

docs/TODO.txt

@@ -275,13 +275,13 @@ It's mostly a bunch of personal notes, probably incomplete. Feel free to query i
 
  - nav: some features such as PageUp/Down/Home/End should probably work without ImGuiConfigFlags_NavEnableKeyboard? (where do we draw the line? how about CTRL+Tab)
  ! nav: never clear NavId on some setup (e.g. gamepad centric)
- - nav: there's currently no way to completely clear focus with the keyboard. depending on patterns used by the application to dispatch inputs, it may be desirable.
  - nav: Home/End behavior when navigable item is not fully visible at the edge of scrolling? should be backtrack to keep item into view?
  - nav: NavScrollToBringItemIntoView() with item bigger than view should focus top-right? Repro: using Nav in "About Window"
- - nav: wrap around logic to allow e.g. grid based layout (pressing NavRight on the right-most element would go to the next row, etc.). see internal's NavMoveRequestTryWrapping().
+ - nav: expose wrap around flags/logic to allow e.g. grid based layout (pressing NavRight on the right-most element would go to the next row, etc.). see internal's NavMoveRequestTryWrapping().
  - nav: patterns to make it possible for arrows key to update selection (see JustMovedTo in range_select branch)
  - nav: restore/find nearest NavId when current one disappear (e.g. pressed a button that disappear, or perhaps auto restoring when current button change name)
  - nav: SetItemDefaultFocus() level of priority, so widget like Selectable when inside a popup could claim a low-priority default focus on the first selected iem
+ - nav: holding space to repeat a button doesn't show button activated during hold.
  - nav: NavFlattened: init requests don't work properly on flattened siblings.
  - nav: NavFlattened: pageup/pagedown/home/end don't work properly on flattened siblings.
  - nav: NavFlattened: ESC on a flattened child should select something.