PY-25001 Implement Complete Current Statement for collection literals

It works by automatically inserting a trailing comma before a line break in
multiline collection literals. Additionally, a colon is inserted between a key
and a value in dict literals.

Because of the language ambiguity regarding syntax of some incomplete collection
literals, colon is not inserted after the first key of a dict literal
(it's indistinguishable from a set literal with one item), and comma is not
inserted after the first item of a parenthesized tuple (it's indistinguishable
from a parenthesized expression).

The idea was taken from such implementation of Complete Current Statement for
JSON.

GitOrigin-RevId: 49ff9857d8c12476bfa9aacaed0b49faa99810fd

python/testData/codeInsight/smartEnter/multilineDictLiteralAfterKeyWithoutColon.py

@@ -0,0 +1,4 @@
+d = {
+  'key1': 1,
+  'key2'<caret>
+}