This commit refactors this page in line with coding standards and linting output and documents the l10n directory.

Done has been deprecated for some time. Then is functionally equivalent and is forward-compatible with api4.

Reorganze Api4 Usage

Updates requirements

Remove pass-by-reference from form variable

My understanding is it's meaningless for objects

Clarify how to setup automatic publishing

Contribution pre/post hooks

Explain when mailingID and messageTemplateID are passed through

Add "Populate Help Text on the Payment Processor Administrator Screen" section

Add better example for transaction handling

Fix extensions' code block

Add in documentation on setting and retrieving contact settings using…

Co-Authored-By: Tim Otten <totten@civicrm.org>

Update explorer url

Add in documentation on setting and retrieving contact settings using the Civi:: facade and also add in note about the deprecation of the ::setItem function

Fix indentation of code block in hook_civicrm_permission

Fixed typo

Incorporate Abandoned Extensions process

Typo fix & SetCheckPermissions example.

tools/issue-tracking.md - Update guidance on Gitlab labels

Add use statement for definition - hopefully people will know that go…

__Before__: The documentation explains ~5 common labels.  Gitlab actually has ~50
labels.

__After__: The documentation explains ~3 important labels and ~4 *prefixes*.
Each prefix is given with a definition and example, and there are links
to the full lists.

__Comment__: The link goes to https://lab.civicrm.org/dev/core/-/labels
though arguably https://lab.civicrm.org/groups/dev/-/labels might be better.
However, there a dozen or so labels which (rightly or wrongly) only show up
in `dev/core`, so `dev/core` gives the more comprehensive listing.

Add link to Abandoned Extensions page/info.