Cherry-pick of #16387 to RC3.6.0_master

Purpose

PR in response to this Slack thread and related to DYN-8893.

Updates to ConnectorViewModel.cs make sure that connectors between two collapsed groups remain visible and render correctly under their proxy ports.

• Updated SetCollapsedByNodeViewModel() to explicitly check if both the start and end ports are proxy ports. If so, the connector is no longer collapsed in this case.
• Removed the unused ConnectingNodesBothInCollapsedGroup() method from SetZIndex() as it was redundant. Even when a connector links nodes inside two collapsed groups, its ZIndex still needs to be 1 to ensure it does not render on top of the proxy ports.

Before:

After:

Declarations

Check these if you believe they are true

• 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
• 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
• This PR contains no files larger than 50 MB
• This PR introduces new feature code involve network connecting and is tested with no-network mode.

Release Notes

Updates to make sure that connectors between two collapsed groups remain visible and render correctly under their proxy ports.

Reviewers

@DynamoDS/eidos
@jasonstratton

FYIs

@dnenov
@achintyabhat
@zeusongit