Variable Injection

## User Story

As a script author, I want to be able to inject my variables in my script within the new script editor, like I used to be able to do with the function browser\.

## Acceptance Criteria

- A user has a way to see a list of their created variables

- A user has a way to inject those variables into their script

- Variable names are injected at the current cursor position

## Notes

- It is not expected that any composition block merging will need to be done with this; if a user injects into the composition block then their sync will be disabled

- This is only a feature parity item with Data Explorer for Variable injection; a bigger feature around the revamp of variables will be a bigger item in a larger EPIC