Refactor naming and usage of Web IDE left-pane related constants

What does this MR do?

This is a refactoring to support a collapsible left sidebar. See the epic for more context: &2585 (closed)

This work has already been done in !21010 (closed), this is just a more incremental approach.

Tasks

Tasks

• rename constants from activityBarViews to leftSidebarViews
• Change structure of constants to match rightSidebarViews
• Replace all occurrences of activityBarViews.key with leftSidebarViews.key.name.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content

Closes #204817 (closed)