Use mock-apollo-provider in SAST UI tests

What does this MR do?

Use mock-apollo-provider in SAST UI tests

Using mock-apollo-provider results in a more realistic test, since the internals of the component(s) (i.e., data) aren't manipulated by the test suite.

This change also removed an unnecessary use of localVue in a related test suite, and moved the SAST spec helpers up a level in the tree.

Addresses #249556 (closed).

Screenshots (strongly suggested)

n/a

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