Only claim the TextInput responder while a touch is active

[lazerg]

Summary:

TextInput passes onSelectionChangeShouldSetResponder={emptyFunctionThatReturnsTrue}, so it takes the JS responder on any selection change the responder system walks. That walk is gated on trackedTouchCount > 0, and the counter counts events rather than touches: press two fingers down separately, lift them together, and it never comes back down, since two starts arrive as two events and the lift arrives as one. From then on every keystroke-driven selection change hands the responder to the focused input with no touch behind it, and the next tap elsewhere is dropped, because negotiation dispatches from the lowest common ancestor of the responder and the new target and so never reaches the new target's own onStartShouldSetResponder.

Claim it only while touchHistory.numberActiveTouches > 0, which is read from touches.length on every start and end and does track the real state. Drag selection keeps working, since a finger is down for the whole gesture.

Fixes #58445. RNTester reproducer in #58449.

Changelog:

[IOS] [FIXED] - TextInput no longer takes the touch responder on a selection change with no active touch

Test Plan:

• yarn lint and yarn flow-check clean, yarn test packages/react-native/Libraries/Components passes
• Not verified on a device, and no test added: the Fantom responder tests are skipped in OSS, so there is nothing here CI would run. Reproducer for #58445: TextInput takes the responder on a keystroke after a two-finger gesture #58449 has the manual steps, which need a physical device (the Simulator lands both fingers in one event and does not reproduce it)