PY-11357 Make automatic surrounding with custom folding comments more robust

* Searching of first parental PSI elements before/after new line
correctly stops at the start/end of file. As result it's possible now
to surround element at the first/last line in the file.
Also corresponding traversal does not try to climb above PSI file.
* Even single character can be selected in first place.
* In languages that uses indentation to delimit blocks (like Python)
several consequent sibling statements can be surrounded even if the last
of them is at the end of its parent.

python/testData/surround/CustomFoldingRegionFirstMethod_after.py

@@ -0,0 +1,17 @@
+class ThisIsATest():
+    # <editor-fold desc="Description">
+    def __init__(self):
+        self.test = 1
+    # </editor-fold>
+
+    def another_one(self):
+        print "Hello, world!"
+
+    def another_two(self):
+        print "Hello, world!"
+
+    def another_three(self):
+        print "Hello, world!"
+
+    def another_four(self):
+        print "Hello, world!"

python/testData/surround/CustomFoldingRegionIllegalSelection.py

@@ -0,0 +1,4 @@
+[
+  1,
+  <selection>2
+]</selection>

python/testData/surround/CustomFoldingRegionIllegalSelection_after.py

@@ -0,0 +1,4 @@
+[
+  1,
+  2
+]

python/testData/surround/CustomFoldingRegionLastMethod.py

@@ -12,4 +12,4 @@ class ThisIsATest():
         print "Hello, world!"
 
     <selection>def another_four(self):
-        print "Hello, world!"</selection>
+        print "Hello, world!"</selection>

python/testData/surround/CustomFoldingRegionLastMethod_after.py

@@ -0,0 +1,17 @@
+class ThisIsATest():
+    def __init__(self):
+        self.test = 1
+
+    def another_one(self):
+        print "Hello, world!"
+
+    def another_two(self):
+        print "Hello, world!"
+
+    def another_three(self):
+        print "Hello, world!"
+
+    # <editor-fold desc="Description">
+    def another_four(self):
+        print "Hello, world!"
+        # </editor-fold>

python/testData/surround/CustomFoldingRegionSeveralMethods.py

@@ -0,0 +1,9 @@
+class C:
+    def m1(self):
+        pass
+
+    <selection>def m2(self):
+        pass
+
+    def m3(self):
+        pass</selection>

python/testData/surround/CustomFoldingRegionSeveralMethods_after.py

@@ -0,0 +1,11 @@
+class C:
+    def m1(self):
+        pass
+
+    # <editor-fold desc="Description">
+    def m2(self):
+        pass
+
+    def m3(self):
+        pass
+        # </editor-fold>

python/testData/surround/CustomFoldingRegionSingleCharacter.py

@@ -0,0 +1 @@
+x = 'foo' <selection>+</selection> 'bar'

python/testData/surround/CustomFoldingRegionSingleCharacter_after.py

@@ -0,0 +1,3 @@
+# <editor-fold desc="Description">
+x = 'foo' + 'bar'
+# </editor-fold>

python/testData/surround/CustomFoldingRegionSingleStatementInFile.py

@@ -0,0 +1,2 @@
+<selection>print('foo')
+</selection>

python/testData/surround/CustomFoldingRegionSingleStatementInFile_after.py

@@ -0,0 +1,3 @@
+# <editor-fold desc="Description">
+print('foo')
+# </editor-fold>