Support diff version and whitespace arguments for diffs batch endpoint

What does this MR do?

It's a next step towards deprecating the regular /diffs endpoint in favor of /diffs_batch.

With this change we can receive pagination arguments at /diffs_batch, even if we fetch diffs from the repository. Though, we won't batch these results yet, which is a work for #32859 (closed). It'll return all content at once, as the regular /diffs.

This mainly avoid using two different endpoints for persisted/batched diffs and repository/non-batch diffs.

#35754 (closed)

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Arguments being supported:

• diff_id
• start_sha
• w (include / ignore whitespace)

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
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• Style guides
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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