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,
+}

python/testData/psi/TabInsideContinuationIndent.txt

@@ -0,0 +1,20 @@
+PyFile:TabInsideContinuationIndent.py
+  PyAssignmentStatement
+    PyTargetExpression: x
+      PsiElement(Py:IDENTIFIER)('x')
+    PsiWhiteSpace(' ')
+    PsiElement(Py:EQ)('=')
+    PsiWhiteSpace(' ')
+    PyDictLiteralExpression
+      PsiElement(Py:LBRACE)('{')
+      PsiWhiteSpace('\n\t')
+      PyKeyValueExpression
+        PyStringLiteralExpression: foo
+          PsiElement(Py:SINGLE_QUOTED_STRING)(''foo'')
+        PsiElement(Py:COLON)(':')
+        PsiWhiteSpace(' ')
+        PyNumericLiteralExpression
+          PsiElement(Py:INTEGER_LITERAL)('42')
+      PsiElement(Py:COMMA)(',')
+      PsiWhiteSpace('\n')
+      PsiElement(Py:RBRACE)('}')