Check for feature status in SnippetsFinder

What does this MR do?

Change SnippetsFinder to halt execution and return Snippets.none if being used with project that has the snippets feature disabled.

This will increase performance when the finder is used, e.g. in NotesFinder or the AutocompleteService and any other future use of the finder.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done