Introduced a mixin for spinner for re-usability

What does this MR do?

1. Converts existing .spinner styles into a re-usable mixin
2. Make use of that mixin for Editor Lite's loading state

Screenshots (strongly suggested)

	Before	After
Blob loading	ScreenFlow3	ScreenFlow2

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

Related to

• #273016 (closed)
• #209090 (closed)