Child of MDL-80971.

Need to make sure the following commits, which touch mod_lti, are also made in the feature branch. Some of this code has been copied to core_ltix (no git move) so rebase won't catch all of these:

Hash: 5d74f366a0ec294b1687637a578b35aebcadcd46
  https://github.com/moodle/moodle/commit/5d74f366a0ec294b1687637a578b35aebcadcd46
  https://tracker.moodle.org/browse/MDL-81172
Hash: 626c3ef5edb6a44f215f412a950ca02c731ea563
  https://github.com/moodle/moodle/commit/626c3ef5edb6a44f215f412a950ca02c731ea563
  https://tracker.moodle.org/browse/MDL-82211
Hash: 4753cf3a36591901123167426371031fa361c8a9
  https://github.com/moodle/moodle/commit/4753cf3a36591901123167426371031fa361c8a9
  https://tracker.moodle.org/browse/MDL-80646
Hash: d0d62fd06c79fd43ab118b1c2fcf88700f162205
  https://github.com/moodle/moodle/commit/d0d62fd06c79fd43ab118b1c2fcf88700f162205
  https://tracker.moodle.org/browse/MDL-75670
Hash: 9beff03a9687dfe72c8231f1329c2f439a38e912
  https://github.com/moodle/moodle/commit/9beff03a9687dfe72c8231f1329c2f439a38e912
  https://tracker.moodle.org/browse/MDL-79626
Hash: 01148a0816a83343b389f0543280ef9bfbffe9df
  https://github.com/moodle/moodle/commit/01148a0816a83343b389f0543280ef9bfbffe9df
  https://tracker.moodle.org/browse/MDL-81522
Hash: f61a764d165426a059072f3b4f7fd519229e3cab
  https://github.com/moodle/moodle/commit/f61a764d165426a059072f3b4f7fd519229e3cab
  https://tracker.moodle.org/browse/MDL-80914
Hash: 018e6e1fc897c2cc1ae545fa411e430b99b3582d
  https://github.com/moodle/moodle/commit/018e6e1fc897c2cc1ae545fa411e430b99b3582d
  https://tracker.moodle.org/browse/MDL-81698