IDEA-80056 Column selection mode improvement

completion behaviour improvements:
* insert generated text into all carets' positions
* apply post-completion actions (like parenthesis insertion) to all carets

java/java-tests/testData/codeInsight/completion/normal/MultiCaretSingleItemInsertion.java

@@ -0,0 +1,4 @@
+class Foo {{
+  ret<caret>;
+  ret<caret>;
+}}

java/java-tests/testData/codeInsight/completion/normal/MultiCaretSingleItemInsertion_after.java

@@ -0,0 +1,4 @@
+class Foo {{
+  return<caret>;
+  return<caret>;
+}}

java/java-tests/testData/codeInsight/completion/normal/MulticaretMethodWithParen.java

@@ -0,0 +1,4 @@
+class Foo {{
+  System.out.ap<caret>
+  System.out.ap<caret>
+}}

java/java-tests/testData/codeInsight/completion/normal/MulticaretMethodWithParen_after.java

@@ -0,0 +1,4 @@
+class Foo {{
+  System.out.append(<caret>)
+  System.out.append(<caret>)
+}}