Auto-link Gutenberg repo mentions in Trac

[pento]

In much the same way as we auto-link user mentions, it'd be super handy to auto-link Gutenberg repo issue numbers.

Personally, I use the form GB12345, which would then link to https://github.com/WordPress/Gutenberg/issues/12345.

There's no need to differentiate between Issues and PRs, GitHub will redirect to the appropriate URL.

[dd32]

This comment serves for testing Github issue mentioning. None of these are linked in the source of the comment.

GB1234
GB-56789
Testing/GB1235/Testing

It shouldn't match these:

• ​Link that shouldn't match or work
• ​GB-56789 Already linked, shouldn't re-link or nest <a>'s.
• ​We're tracking this in GB-56789 already

[dd32]

In 8054:

Trac: Autolink Gutenberg Github issues using the form GB-1234 or GB1234.

Fixes #3961.

[dd32]

In 8055:

Trac: Tweak the regex in r8054 to avoid matching references contained within a link that mentions it part-way through the link text.

See #3961.

[dd32]

In 8056:

Trac: Bump the cache busters after r8054 & r8055.

Fixes #3961.