IDEA-63303 Collapsing of multiline //-style comment feature request

1. Added ability to configure IJ editor to auto-collapse multiple subsequent end of line comments;
2. Corresponding test is added;

java/java-tests/testData/codeInsight/folding/EndOfLineComments.java

@@ -0,0 +1,14 @@
+class Test {
+  
+  <fold text='//...'>// class-level folding1
+  // class-level folding2</fold>
+  
+  public void foo() <fold text='{...}'>{
+    <fold text='//...'>// method-level folding1
+    // method-level folding2</fold>
+    int i = 1;
+    // method-level folding2
+  }</fold>
+
+  // class-level folding3
+}