Support sending visual context to Smartling, for its CAT tool

[stevejalim]

One-line summary

This changset adds support for sending a visual context (a HTML document + relevant URL) to Smartling so that the CAT "live translation preview" tool can be used easily.

Significant changes and points to review

• Adds a callback for wagtail-localize-smartling to send visual context to Smartling

• Updates our wagtail-localize-smartling and wagtaildraftsharing dependencies, to enable the callback mentioned above to be used (and also to generate a useful URL with it)

Issue / Bugzilla link

Resolves #14938

Testing

I've tested this with @cocomo over a Zoom call, so code-level review here is enough

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.81%. Comparing base (9d4487e) to head (4244edd). Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...edrock/cms/wagtail_localize_smartling/callbacks.py	90.47%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #15519 +/- ## ========================================== + Coverage 78.78% 78.81% +0.02% ========================================== Files 157 158 +1 Lines 8257 8278 +21 ========================================== + Hits 6505 6524 +19 - Misses 1752 1754 +2 ```

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