allow turning off auto tracking of active pane

[bobjunga]

Description of the Change

Enhance the tree-view config to allow turning off the behavior to change the tree selection when the active pane item changes.

Moved tree-view:autoReveal config into a config object that also has an enable boolean

tree-view:autoTrackActivePane
    |  enable
    '  autoReveal

tree-view's onDidChangeActivePaneItem handler now 1) migrates the old autoReveal to new autoTrackActivePane.autoReveal (if its present) and 2) uses autoTrackActivePane.enable to decide whether to call selectActiveFile and revealActiveFile

• closes Add config to determine if tree selection changes when editor changes  #1335
• the defaults are Enabled:true, AutoScroll:false which maintains the same default behavior as before this change.
• it migrates the old autoReveal if its present in the config.
  • migration is required not only to keep the user's preference, but also we need to call unset on it so that the Settings View does not keep displaying it even though its no longer in the schema.
• note that I also changed the description of the "Focus On Reveal" config to make it clear that it does not affect Auto Reveal but just the Reveal Active File command.

Alternate Designs

Considered changing autoReveal to an enum. See #1335

Benefits

Backward compatible with previous behavior and now allows a new behavior. See #1335

Possible Drawbacks

If other packages use tree-view:autoReveal they should eventually be updated to use autoTrackActivePane.autoReveal instead but in the mean time the impact should not be severe. If they enable autoReveal, it will still take effect because of the migration condition in the code.

Applicable Issues

#1335