Move "Show latest version" button to the left

What does this MR do?

The buttons at the top of the Merge Request diff view are a bit all over the place. This change is one step to make them be more intuitive, as part of #330579.

The "Show latest version" button was a bit out of place being between the diff stats and diff preferences.

This change moves that button to the left. It now sits right next to the commit Prev/Next buttons or version dropdowns. This brings the buttons which control the range of the diff together.

Issue: #330579

Screenshots (strongly suggested)

On single commit

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After

On older version in MR

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After

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
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• This change is backwards compatible across updates, or this does not apply.

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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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