PY-20003 Fixed: Breadcrumbs for Python files

Introduce PyBreadcrumbsInfoProvider which supports:
classes and functions (incl. async) definitions,
lambdas, try-except-else-finally, if-elif-else,
for-else (incl. async), while-else, with and
key-value statements

python/testData/breadcrumbs/asyncFor.py

@@ -0,0 +1,3 @@
+async def foo():
+    async for i in range(10):
+        print(<caret>i)