mostly completed "register extension" fix (IDEA-60730)
consistent search scope when resolving plugin classes from plugin.xml [r=peter]
honor <with> element in plugin.xml dom
look at @Attribute(name="") when resolving <with attribute="">
inspection and quickfix to add <with> tags to <extensionPoint> declarations
recognize more key fields
auto-suggest class name for <with implements=""> attribute
cut EP name after last dot when guessing implementation class name
add <with> tags to platform extension points
show chooser when there are multiple candidates for extension point registration
separate "tag" and "attribute" attributes on <with> tag; correctly create extension registration when class name is specified in a subtag (IDEA-60730 done)