[3.x] Fix problems in lexicon creation form

[smg6511]

What does it do?

Made changes to lexicon processors to add simple validation logic and changed js form to make certain fields required.

Why is it needed?

As there is currently no validation of lexicon form values, records without all the required data save to the database but cannot display because of missing information.

How to test

Test this under two conditions:

1. Disable the allowBlank properties I added to the js form; in this way you can verify that the basic php validation works when trying to create a lexicon entry with one or more blank values.
2. Re-enable the allowBlank properties and to verify that the front end validation stops the form from submitting when required values are missing.

Note: Now only valid entries will be saved, so they will always be found in the grid when using the filtering toolbar.

Related issue(s)/PR(s)

Addresses issue #15223.

[Mark-H]

Tested and seems to work, but it may be worth fixing up the array_map trim.