JoinLines: better comments processing

1. Improve the support of other languages in CommentJoinLinesHandler
2. Respect right margin in CommentJoinLinesHandler
3. JoinLineProcessor#convertEndComments: do not convert if only whitespaces are going to be added
4. JoinLineProcessor#adjustWhiteSpace: do not add white-spaces before line-break
Also fixes IDEA-125325 Join lines in custom file type should handle end-of-line comments

GitOrigin-RevId: 392fe2455dcf19d21303a0b42ee85db7f824fa85

java/java-tests/testData/codeInsight/joinLines/ConvertFinalLineComment2.java

@@ -0,0 +1,8 @@
+class A {
+  <selection>// foo
+
+
+
+  </selection>
+
+}