chore: fix namespacing issues in 4.2+

[matthewhilton]

• Fixes externallib and context class namespaces by including necessary lib which has class aliases for older moodle versions (i.e. < 4.2)
  • See https://tracker.moodle.org/browse/MDL-76583 and https://tracker.moodle.org/browse/MDL-74936 for info
• Add ci since it was missing 👻

[matthewhilton]

The upstream CI issue has been resolved, so now the CI is running properly. Unfortunately there are lots of pre-existing code standards errors that are out of scope to fix here.

However, the failing tests in 4.4 that prompted this change have been resolved:

4) core_external\external_api_test::test_all_external_info with data set "mod_hvp_log_drain" (stdClass Object (...))
Error: Class "external_api" not found
5) core_external\external_api_test::test_all_external_info with data set "mod_hvp_submit_mobile_finished" (stdClass Object (...))
Error: Class "external_api" not found

Confirmed resolved via CI unit tests + also I have tested manually current main + 4.1 branch and it maintains compatibility with both.