PY-14408 PythonIndentingProcessor includes tabs inside PsiWhitespace elements

Also I partially reverted previous fix in PyBlock#isWhitespaceLineBreaks,
because current approach is more general and that workaround is no longer
needed (multiple whitespaces are collapsed into single element as in other
languages).

python/testData/psi/TabInsideContinuationIndent.py

@@ -0,0 +1,3 @@
+x = {
+	'foo': 42,
+}