Revert: fix(widgets): dismiss open RawTooltip on Escape key (WCAG 1.4.13) - #193183

….13)" (flutter#193192)

Relands flutter#192966 (reverted in
flutter#193183) with `OverlayEntry`
disposal in `raw_tooltip_test.dart` and `FocusManager` early key-event
interception in `raw_tooltip.dart`.

### What changed since flutter#192966 (`f8c85519a060`)

1. **Test `OverlayEntry` Leak Fix (`raw_tooltip_test.dart`)**:
- In `raw_tooltip_test.dart` (`Escape key dismisses hovered RawTooltip
even when primaryFocus is on a sibling consuming Escape`), `flutter#192966`
passed an inline `OverlayEntry(...)` to `Overlay(initialEntries:
<OverlayEntry>[...])` without calling `entry.remove()` and
`entry.dispose()` in `addTearDown`. Because `Overlay` does not dispose
`initialEntries` on unmount, the `OverlayEntry`'s internal
`ValueNotifier<_OverlayEntryWidgetState?>` was flagged as `notDisposed`
by `leak_tracker` in CI (`Linux framework_tests_widgets_leak_tracking`).
- This reland captures `OverlayEntry? entry` and registers
`addTearDown(() { entry?.remove(); entry?.dispose(); })`. Verified
locally with `flutter test --dart-define=LEAK_TRACKING=true
test/widgets/raw_tooltip_test.dart`.
2. **Stop `Escape` Propagation Before Focus-Tree Shortcuts
(`raw_tooltip.dart`)**:
- In `flutter#192966`, `RawTooltipState` registered
`HardwareKeyboard.instance.addHandler(_handleKeyEvent)` alone. Because
`KeyEventManager` runs `HardwareKeyboard` handlers *before*
`FocusManager.handleKeyMessage` without stopping the focus-tree walk
when returning `true`, emptying `RawTooltip._openedTooltips` in
`HardwareKeyboard` caused `Escape` to still reach focused siblings
(`siblingReceivedEscape`) or `WidgetsApp`'s `Shortcuts` (`DismissIntent`
on enclosing `ModalRoute`s such as `DatePickerDialog`).
- This reland registers a single static pair
(`FocusManager.instance.addEarlyKeyEventHandler(_handleEarlyKeyEvent)`
plus `HardwareKeyboard.instance.addHandler(_handleHardwareKeyEvent)`
fallback when `primaryFocus == null`) when `RawTooltip._openedTooltips`
transitions from empty to non-empty, and removes them when the last open
tooltip closes or disposes. Returning `KeyEventResult.handled` from
`_handleEarlyKeyEvent` stops `FocusManager` before walking the focus
tree, and a second test (`Escape key dismisses open RawTooltip inside
WidgetsApp without invoking ancestor DismissIntent`) verifies both
cases.

### Original description

Fixes http://b/463905826

WCAG 1.4.13 (Content on Hover or Focus) requires a mechanism to dismiss
additional content triggered by pointer hover or keyboard focus
(`Escape` key) without moving pointer hover or keyboard focus, and
without unintended side effects such as dismissing an enclosing modal
dialog (`DatePickerDialog`) when a tooltip is open.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] All existing and new tests are passing.