[Gallery Block]: A11y - Add and Update missing reduce-motion mixing - mostly depreciated

[Mayank-Tripathi32]

Part of #68282

Considerations

The code is largely deprecated, so I'm unsure if this PR is necessary, especially since we might be cleaning up the CSS soon.

What?

Refactors animation and transition styles to use @media not (prefers-reduced-motion) for improved accessibility, ensuring a better experience for users who prefer reduced motion.

Why?

Currently, many parts of the codebase do not consider users' motion preferences, which may not be ideal for those with reduced motion settings. This PR addresses and fixes that issue.

How?

This PR updates the old reduce-motion mixin implementation and addresses missing cases to adopt the new approach outlined in the parent issue.

	@media not ( prefers-reduced-motion ) {
			transition: opacity 0.1s linear;
		}

Standard adopted from @wordpress/components

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[t-hamano]

Closing as a duplicate of #68315.