fix(QTooltip): show on keyboard focus & dismiss with ESC (fix #18241)

[arbaev]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Documentation
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the dev branch
• When resolving a specific issue, it's referenced in the PR's title (fix #18241)
• It's been tested on a Cordova (iOS, Android) app
• It's been tested on an Electron app
• Any necessary documentation has been added or updated, or explained in the PR's description

Other information:

Fixes #18241.

Problem

QTooltip only showed on mouse hover (and touch), so keyboard-only users never saw it when tabbing to the target — a violation of WCAG 1.4.13 (Content on Hover or Focus).

Change

In the tooltip's anchor wiring (desktop):

• Show on keyboard focus of the target, gated by :focus-visible so the tooltip does not appear on plain pointer clicks (mouse users keep hover).
• Hide on blur.
• Dismiss with ESC while shown, via Quasar's shared escape-key stack (same mechanism as QMenu/QDialog) — only the top-most popup reacts and focus is not moved (WCAG "dismissible").

No new props/events; respects the existing noParentEvent and persistent.
The touch/mobile path is unchanged.

Scope / note

A focusable trigger is required (QBtn, links, inputs…). A tooltip on a non-focusable element (a bare <div> without tabindex) still can't receive focus — that remains the app's responsibility.

Verification

Built from source and exercised in headless Chromium (Playwright):

• idle: no tooltip
• Tab focuses target → shown
• ESC → hidden, focus stays on target
• blur (Tab away) → hidden
• mouse hover → shown / mouse leave → hidden
• mouse click (focus without :focus-visible) → not shown

Cordova/Electron not separately tested — the change uses standard DOM focus/blur + :focus-visible and the existing escape-key stack, with no platform-specific code. No unit test added: QTooltip currently has no test file and the spec harness requires full-API coverage for any existing test file; the :focus-visible gating also can't be exercised under jsdom.
Happy to follow up with full QTooltip test coverage separately.