Add common JetElement for imports: JetImportList

idea/testData/folding/afterOptimizeImports/foldingAfterOptimizeImportsRemoveFirst.kt

@@ -0,0 +1,12 @@
+package sometest
+
+import java.util.ArrayList
+import java.util.HashSet
+import java.util.HashMap
+
+val some: HashSet<Int>? = null
+val some2: HashMap<Int, Int>? = null
+
+// SET_TRUE: setCollapseImports
+// REGION BEFORE: 25:94
+// REGION AFTER: 25:67

idea/testData/quickfix/override/nothingToOverride/import.before.Main.kt

@@ -2,6 +2,7 @@
 // ERROR: 'f' overrides nothing
 // ERROR: 'f' overrides nothing
 import a.B
+
 class BB : B() {
     <caret>override fun f() {}
 }

idea/testData/quickfix/typeImports/afterHasThisImport.kt

@@ -2,14 +2,10 @@
 package a
 
 import java.util.Collections
-
-package b {
-
 import java.util.List
 
 class M {
     trait A {
         val l: jet.List<Int><caret>
     }
-}
 }

idea/testData/quickfix/typeImports/beforeHasThisImport.kt

@@ -2,14 +2,10 @@
 package a
 
 import java.util.Collections
-
-package b {
-
 import java.util.List
 
 class M {
     trait A {
         val l = <caret>Collections.emptyList<Int>()
     }
-}
 }