Purpose

Removes the 500 units bound on the extension panel width. The panel can
be enlarged as much as needed, while respecting the minimum size of the
canvas panel, which remains as 200 units.

Also, the extension panel size is remembered during a session. Serves
both as a nice to have and a avoids a splitter bug.

Also, the workspace references extension is fixed so that it adapts to
bigger sizes. It didn't stretch beyond 600 units.

Declarations

Check these if you believe they are true

• The codebase is in a better state after this PR
• Is documented according to the standards
• The level of testing this PR includes is appropriate
• User facing strings, if any, are extracted into *.resx files
• All tests pass using the self-service CI.
• Snapshot of UI changes, if any.
• Changes to the API follow Semantic Versioning and are documented in the API Changes document.
• This PR modifies some build requirements and the readme is updated

Reviewers

@QilongTang @reddyashish

FYIs

@DynamoDS/dynamo