Add configurable timeout parameter to flashBlock

[karthick-murugan]

Closes #71751

What?

This PR updates the flashBlock action in packages/block-editor/src/store/actions.js to support a configurable timeout duration.

Previously, the highlight duration was fixed at 150ms, which could feel too fast in some contexts. With this update, flashBlock accepts an optional timeout parameter, allowing developers to control how long the highlight remains visible.

Why?

1. Provides flexibility for different UX needs (e.g., comments sidebar navigation vs. quick copy confirmation).
2. Keeps backward compatibility by defaulting to 150ms when no timeout is specified.

Testing Instructions

Trigger flashBlock( clientId ) → should behave as before (150ms).

Trigger flashBlock( clientId, 1000 ) → highlight should remain visible for ~1 second.

cc @t-hamano

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Co-authored-by: karthick-murugan <[email protected]>
Co-authored-by: adamsilverstein <[email protected]>
Co-authored-by: t-hamano <[email protected]>
Co-authored-by: Mamaduka <[email protected]>

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[adamsilverstein]

Looks good to me!

[adamsilverstein]

@Mamaduka / @t-hamano are we ok to merge this?

[t-hamano]

I'm in favor of this enhancement, but I want to be careful because it's a public API. Let's mention the people involved in #22186, where the flashBlock was added. cc @mcsf @youknowriad @ellatrix

[Mamaduka]

This should be good to merge. The default behavior remains the same, while allowing duration to be changed.

[t-hamano]

@Mamaduka Thanks for the feedback! Well, let's merge this PR.