fix: clear text selection when user taps outside the view

[haileyok]

Summary

Fixes #36.

A non-editable, selectable UITextView does not auto-resign first responder on outside tap, so the text selection persists indefinitely. This adds a window-level UITapGestureRecognizer that fires on taps anywhere outside the component's bounds and clears selectedTextRange.

Notes on the design:

• cancelsTouchesInView = NO so the tap still reaches whatever the user actually tapped (button, scroll view, etc.).
• gestureRecognizer:shouldReceiveTouch: filters via hit-test so the recognizer only fires when the touch is not a descendant of self — taps inside our own text view are handled by UITextView itself.
• The actual selectedTextRange = nil is wrapped in dispatch_async(dispatch_get_main_queue(), …) so any in-flight edit-menu action (Copy / Define / Look Up / Share / …) gets to read the live selection before we drop it. Without the defer, on iOS ≤15 the tap on a UICalloutBar button can race the action handler and Copy ends up with an empty pasteboard.
• The recognizer is attached in didMoveToWindow and removed when the view leaves the window or is dealloc'd, so view recycling stays clean.

Test plan

• Select text in a <UITextView selectable uiTextView>, tap empty space outside it — selection clears.
• Select text, tap Copy in the edit menu — text is copied to the pasteboard, then selection clears.
• Select text, tap a button elsewhere — button action fires AND selection clears.
• Two <UITextView selectable uiTextView> on the same screen — selecting in one then tapping the other clears the first.
• Inside a ScrollView, scrolling does not clear the selection (it isn't a tap).
• Recycle a list of selectable text views (e.g. in a FlatList) — no crash, no leaked recognizers.

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