cleanup one test and workingset view extensibility
mutable file object for wsv item class
fix comment
rework classes array
allow refresh to update the class list without rebuilding the entire view
update doc to support jQuery for IconProvider
update comment
update comment again
remove unused var in test
- filter only [Extension] console output for the ExtensionLoader tests
merge with master
rtc:nits
Merge branch 'master' into jeff/wsv-extensibility
Fix a case in which an expanded subdirectory causes parent from loading fully.
Save tree state when folders are toggled via toggleSubdirectories and closeSubtree.

Fix for #9269.
Save tree state via show in file tree.

Fix for #9276.
- guard against null and non string arguments passed to console.error
Merge pull request #9054 from adobe/jeff/wsv-extensibility

Working Set View Extensibility
Merge pull request #9243 from adobe/ingo/improve-extensionloader-tests

Make ExtensionLoader tests more robust by only validating relevant console output
`.then` for toggleSubdirectories should saveTreeState at the correct time.