Add Collapse All action to SCM view pane

[dmitrivMS]

Fixes #161929

[Copilot]

Pull request overview

This PR adds a "Collapse All" action to the SCM view pane that mimics the behavior found in the Explorer view. The action appears in the context menu when right-clicking on resource groups and intelligently collapses tree nodes in two stages: first collapsing second-level and deeper nodes, then collapsing first-level nodes only if everything below is already collapsed.

Key Changes:

• Added CollapseAllAction class that registers a context menu action for resource groups
• Implemented collapseAllResources() method to handle the two-stage collapse logic
• Action uses the collapseAll Codicon and appears in the 'inline' group of MenuId.SCMResourceGroupContext

[lszomoru]

Thanks for the pull request. Here is some feedback:

1. I think that the action should never collapse the resource group itself (that is what the twistie is for)
2. I think that the action should only be shown if the resources are being shown as a tree
3. Not sure about the position of the action, as it appears the leftmost action

[dmitrivMS]

Thanks for the pull request. Here is some feedback:

1. I think that the action should never collapse the resource group itself (that is what the twistie is for)
2. I think that the action should only be shown if the resources are being shown as a tree
3. Not sure about the position of the action, as it appears the leftmost action

Sounds good, let me rework this, meanwhile will move to Jan milestone.

[dmitrivMS]

@lszomoru Addressed all feedback.