[Feature Request] Quick variable editing

**Is your feature request related to a problem? Please describe.**
Editing variables currently take at least 3 clicks:
- The environments dropdown
- Manage Environment button
- (Select environment)
- Click inside the text field

**Describe the solution you'd like**
When clicking on a variable, in the "Edit Variable" dialog, should have a quick way to change the variable. This would be simpler:
- Click variable where it's used
- Click field

Would be either below or above the preview:

**Describe alternatives you've considered**
Can't think of any simple solution that would be low effort like this one.

Start by tracing how clicking a variable opens the "Edit Variable" dialog and how the variable preview is rendered. Determine where a field for quick editing could fit below or above the preview, then verify that clicking a variable, editing its value, and saving updates the variable where it is used.

Written by the indexing model from the issue text.