fix(textarea): place initial caret at end

[Elements2720]

Summary

Fixes #31579

ion-textarea now renders its initial value through the native value property instead of a text child, matching ion-input.

This makes setFocus() place the initial caret at the end and preserves an existing selection during unrelated renders.

Evidence

• Before: an initial value rendered as textarea text content and setFocus() placed the caret at position 0.
• After: focused caret regression passed with selection [11, 11].
• Selection-preservation regression passed with selection [1, 4] after an unrelated render.
• Focused Mobile Chrome e2e: 4 passed.
• Related input and textarea specs: 17 passed.
• Core build: passed.
• Full npm test: one unrelated existing failure in src/components/datetime/test/disabled/datetime.spec.tsx (expected 4 picker columns, received 3); all other reported suites passed.

Merge Danger

Door: two-way

Blast Radius: textarea

The change is limited to native textarea value initialization and its regression coverage.

[vercel]

@Elements2720 is attempting to deploy a commit to the Ionic Team on Vercel.

A member of the Team first needs to authorize it.