Minor: remove warnings
Introduce utility method for working with multifile tests
Fix invalidating built-ins psi in consecutive test runs
Add structure view source roots
Tests for file structure
Revise JetStructureViewElement

- remove 'my' prefix
- inline ItemPresentation
- use descriptor renderer instead of custom one
Set up rendering for structure elements
Enable members sorting in file structure view
Show members from supertypes in file structure view (KT-4448)

 #KT-4448 Fixed
Add location string showing where method or property is defined
Better caching: do not recount when field true value is null
Fix empty name for class initializer in project view when "Show Members" enabled
Tune location string in structure view
Show delegated methods when "Show inherited" enabled in file structure view
Tests for showing synthetic methods in file structure view
Test for showing kotlin enums with "Show Inherited" option enabled in file structure view
Don't add space if it has been already added