Apply placeholder delay only on Android devices

[12joan]

Description
In PR #5368, a 300ms delay was added before showing the placeholder to prevent issues relating to mobile phone keyboards. This isn't great UX, and as far as I can tell (@edhager Can you confirm?) it's only needed on Android devices. This PR reduces the delay to 0ms on non-Android devices.

Example

recording.mp4

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: e7574ca

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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[12joan]

These Playwright tests fail consistently on CI, but pass for me locally.
https://github.com/ianstormtaylor/slate/actions/runs/6948575390/job/18904830308?pr=5564#step:4:15035

Same result on a branch identical to main, so not a problem with this PR.
https://github.com/12joan/slate/actions/runs/6948704391/job/18905240710#step:4:15020