Adds "Copy" command to many items on the graph

- Avoids polluting GitReference with graph specific data
 - Avoids Git tips ordering for proper group context
 - Reworks group context to merge with base context

* Added icons to hide and show ref nodes of the graph

* Added context menu option to hide branches

* Moved "Hide branch" option to the bottom of the menu

* Changes from code review, including

 - Renames some events/methods
 - Fixes context menus
 - Removed unnecessary debounce

* Validate the hidden refs against the real set of refs

* Typed "refType" property  and added to our d.ts file instead of using an string

* Created a "graph only" wrapper for the GitBranchReference rather than adding it to the general model

* Graph exposed event when hiding refs has been modified to accept a list of hidden refs

* Generic context menu when right-click on the overall ref to hide the whole ref.

* Commented hidden refs validation for v13, as it has too much performance impact. Will be solved after we launch v13 as tech debt

Controls how the Commit Details view is shown by the graph
Honors avatar setting in remote icons

Adds graph context menus for virtual GitHub repos
Adds comparison commands to the graph
Fixes `when` clause contitions for some commands

Adds ref PR context menus

Adds Open Details to commits & stashes in views

Hides commit graph icon in hovers if plus features are disabled

Optimizes startup flow and churn during discovery

e.g. branches, commits, stashes, tags

* 73 - Graph allow user to toggle some features in settings

* Modified name of "enableGhostRefs" property to be "showGhostRefsOnRowHover" instead

Adds search cancellation to avoid needless calls
Adds search limit setting for the Graph

Adds graph.commitOrdering setting

Until the VS Code marketplace can truly handle pre-releases we can't adopt the current limited pre-release provided by VS Code