Add folding doc and multiline comments

idea/testData/folding/checkCollapse/headerKDoc.kt

@@ -0,0 +1,11 @@
+<fold text='/**...*/' expand='~false~'>/**
+ * Some header kdoc
+ */</fold>
+package some
+
+<fold text='/**...*/' expand='true'>/**
+ * Other
+ */</fold>
+
+// SET_TRUE: setCollapseFileHeader
+

idea/testData/folding/checkCollapse/headerMultilineComment.kt

@@ -0,0 +1,12 @@
+<fold text='/.../' expand='~false~'>/*
+ * Some header
+ */</fold>
+
+val a = 12
+
+<fold text='/.../' expand='true'>/*
+ * Other
+ */</fold>
+
+// SET_TRUE: setCollapseFileHeader
+

idea/testData/folding/checkCollapse/imports.kt

@@ -0,0 +1,8 @@
+package some
+
+import <fold text='...' expand='~false~'>first
+import second</fold>
+
+trait A
+
+// SET_TRUE: setCollapseImports