ValidVariableNameSniff: freshen allowed globals

[jrchamp]

• Group by global type with comment.
• Add comment to removed globals.
• Add missing FULLSCRIPT literal.
• Add missing XMLDB object.

Fixes #181

I didn't remove any that were already present, but I have opinions. 😈

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.11%. Comparing base (89ff0ac) to head (40b7ef1).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #182 +/- ## ========================================= Coverage 98.11% 98.11% Complexity 952 952 ========================================= Files 40 40 Lines 2818 2818 ========================================= Hits 2765 2765 Misses 53 53 ```

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