Vimeo: add new shortcode format

[jeherve]

Fixes #14279

Changes proposed in this Pull Request:

We previously only supported 2 main shortcode formats:

• the old format (w=350&h=500) that relies on shorthand for width and height (w and h), with all shortcode attributes in one string separated by &
• the new format (width=350 height=500) that relies on the full words

However our implementation unofficially supported a third, mixed format,
with the w and h shorthand supported in the new format.

This commit makes that third format official.

Testing instructions:

• Do all Unit Tests pass?
• In a new post, try inserting the following shortcodes:
  [vimeo 368043020 w=640 h=360]
[vimeo 368043020 w=640&h=360]
[vimeo 368043020 width=640 height=360]
• All three should work.

Proposed changelog entry for your changes:

• Vimeo: add new shortcode format.

[matticbot]

Caution: This PR has changes that must be merged to WordPress.com
Hello jeherve! These changes need to be synced to WordPress.com - If you 're an a11n, please commandeer, review, and approve D37944-code before merging this PR. Thank you!

[jetpackbot]

Thank you for the great PR description!

When this PR is ready for review, please apply the [Status] Needs Review label. If you are an a11n, please have someone from your team review the code if possible. The Jetpack team will also review this PR and merge it to be included in the next Jetpack release.

Scheduled Jetpack release: January 23, 2020.
Scheduled code freeze: January 16, 2020

Generated by 🚫 dangerJS against b8686d1

[kraftbj]

All three examples worked on a fresh site. 🚢

[jeherve]

r201918-wpcom