fix lost stereotype in AbstractMainNode chooser #MPS-18541 fixed
fix loading plugins in mps tests #MPS-18815 fixed
fix switching between threads on all-thread breakpoint #MPS-18809 fixed
fix per-thread breakpoints #MPS-18829 fixed
Merge branch 'MPS3.0'

Conflicts:
	plugins/debugger-java/runtime/source_gen/jetbrains/mps/debugger/java/runtime/engine/events/ContextManager.java
	plugins/debugger-java/runtime/source_gen/jetbrains/mps/debugger/java/runtime/state/PausedJavaUiState.java
	plugins/execution-languages/languages/library/source_gen/jetbrains/mps/execution/lib/ui/NodeChooser.java
fix compilation