Static templates: also support .jinja files

[jayaddison]

Feature or Bugfix

• Feature

Purpose

• Allow themes and other extensions that utilise the static template functionality to use the suggested (note: not strictly required) .jinja extension for templates.
• The originating motivation I have for this feature is to eventually remove a catch-all missing-suffix expectation in coveragepy that can cause warnings to be emitted when non-Python files are treated as potentially containing Python bytecode for coverage evaluation (ref [low-prio] Possible bug: files without extensions misidentified as Python? coveragepy/coveragepy#1488).

Detail

• When considering whether to render a file using Jinja, check for either the existing already-supported _t suffix or secondly for the additionally-supported .jinja suffix.
• These changes currently target version 7.3 of Sphinx, but I'd be fine with waiting until a future version to introduce them.

Relates

• Re-attempts previous pull request Support and prefer .jinja to _t for static templates #11165 - this time without deprecation notices or a deprecation schedule.

[AA-Turner]

Can we split adding support for .jinja and renaming the internal template files to two PRs?

[jayaddison]

Can we split adding support for .jinja and renaming the internal template files to two PRs?

That seems reasonable, yep. I've restored the original template file paths in this branch.

This could be a case where I'd consider rebasing the commits here. It doesn't seem to make a practical difference given that the changes will be squashed, but somehow it feels odd to have two changes that combine into a no-op in a merged PR.

[chrisjsewell]

Definitely agree with this by the way, I was just thinking the other day that I wanted these templates to be compatible with https://marketplace.visualstudio.com/items?itemName=samuelcolvin.jinjahtml
(Haven't reviewed the actual code yet though)

[jayaddison]

Thank you @AA-Turner!