[datsiuk-ck]

Motivation

An empty, unfocused TextInput with a label was missing from the accessibility tree on iOS and Android, so screen readers skipped it until someone focused it. Every untouched form started in this state. The input's wrapper took the label's float opacity, which is 0 while the label rests, and both platforms drop views with opacity 0 from accessibility.

This PR:

• Keeps the input at full opacity while the label rests (it is empty and its placeholder is blank, so nothing visible changes), and fades it in only once the label floats, as before.
• Always applies that style (opacity 1 without a label). Before, a field focused once and then left without a label kept a stale opacity of 0, so its placeholder and typed text were invisible.
• Rests the placeholder at '' instead of ' '. Once the field was reachable, TalkBack announced it as "Space, edit box" instead of its label. iOS multiline fields keep ' ' (TextInput placeholder remains empty when multiline is true and the placeholder is set after certain timeout react/react-native#31573).

Related issue

Fixes #5197

Screenshots / Videos

Screen readers for unfocused text input

	Before	After
Android	Impossible to select a field with a screen reader:
iOS	Impossible to select a field with a screen reader:

Label removed after the field was focused once, then typing "hello":

	Before	After
Android
iOS

Test plan

1. Render <TextInput label="Email" supportingText="We never share it" placeholder="you@example.com" value={email} onChangeText={setEmail} /> and leave it empty.
2. Android with TalkBack on: touch the field. It is announced as "Email, We never share it, you@example.com. Edit box".
3. iOS simulator with Accessibility Inspector: point at the field. It is a text field labelled "Email, We never share it, you@example.com".
4. Focus the field: the placeholder and any prefix/suffix still fade in as the label floats. Same for a multiline field.
5. Repro from the issue: focus the field, blur it while empty, remove the label, focus and type. The placeholder and the typed text show.

[github-actions]

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