Use CSPELL to fix spelling errors and add custom dictionary

Starting position
CSpell: Files checked: 176, Issues found: 723 in 114 files

The downloaded file of spelling errors has precisely 100 words.

Added .cspell.json and included two core dictionaries. This reduced the errors
CSpell: Files checked: 176, Issues found: 195 in 59 files

The number of unrecognised words reduced to 69

After the gitlab_templates issue #3422323: Improve CSPELL the top-level files are now being checked, when they were being ignored before. The current position is:

CSpell: Files checked: 195, Issues found: 191 in 60 files
The number of unrecognised/misspelled words is 87

CSpell: Files checked: 195, Issues found: 15 in 6 files
The number of unrecognised/misspelled words is 5

I am not going to add the five "misspelled" words to the custom dictionary right now as that would simply hide what I think needs investigation. The five words are

• parms - this is part of variable name in src/Form/SchedulerAdminForm.php $message_parms. I want to know if sub-parts of variable names really have to be full words
• randomstring - is a function call: 'name' => $values['title'] ?? $this->randomstring(12), so are all function names forced to be real words?
• tnid is part of array key in schema.yml 'tnid' => [ The keys nid and vid are not reported because the min word length is 4
• unrequired is a real word, in the Oxford English Dictionary and Merriam Webster so should be in one of the cspell dictionaries
• vals is a var in js/scheduler_vertical_tabs.js var vals = [];

Starting point for 8.x-1.x
CSpell: Files checked: 117, Issues found: 166 in 50 files
The number of unrecognised/misspelled words is 69

All spelling errors fixed in 2.x and 1.x

The README "ignore" comments work for ignoring the words, but the comments are rendered in the file. The correct comment style is <!--- cSpell:disable --->
See https://git.drupalcode.org/project/gitlab_templates/-/merge_requests/202...