Add style guide rules to tests, cross-link

What does this MR do?

While proposing a test for unclear antecedents, I noticed:

• some items on the word list had tests, but weren't cross-linked
• a few items on the word list were missing from tests but easy to add to existing tests

I found a few items that were relatively easy to resolve:

• Rule against the spelling e-mail wasn't in a substitution test, but was an easy addition to SubstitutionSuggestions.yml
• Rule for using we recommend instead of it is recommended or GitLab recommends wasn't in a test, but was an easy addition to SubstitutionSuggestions.yml
• handy, simple, simply, useful were already tested for in Simplicity.yml but the word listed needed to cross-link to the test
• sub-group was already tested for in SubstitutionSuggestions.yml but the word list needed to cross-link to the test
• utilize wasn't in a substitution test, but was an easy addition to SubstitutionWarning.yml (I have no problem with moving it down to SubstitutionSuggestions.yml instead)

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have added information for database reviewers in the MR description, or it's not needed. (Does this MR have database related changes?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.

Security

Does this MR contain changes to processing or storing of credentials or tokens, authorization and authentication methods or other items described in the security review guidelines? If not, then delete this Security section.

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team