Discard NotImportantViews only for XPath & DumpWindow

When setCompressedLayoutHeirarchy is enabled, views not marked as important to accessibility are discarded. This must be enabled for XPath and page source to work. If it's left enabled then it's not possible to find unimportant elements via other locator strategies.

If the discard is toggled back to false at the end of an XPath request it will break XPath. A find request for non-xpath will restore discard to false.

Thanks @paymand for figuring out how to make this work!