New J2K: do not find import usages in AST building phase

It is a rather heavy operation and it increases conversion time
Related to #KT-31848

nj2k/testData/newJ2k/issues/kt-1048.kt

@@ -1,6 +1,8 @@
 // ERROR: The integer literal does not conform to the expected type CapturedType(*)
 // ERROR: The integer literal does not conform to the expected type CapturedType(*)
 // ERROR: Type argument is not within its bounds: should be subtype of 'String?'
+import java.util.HashMap
+
 internal class G<T : String?>(t: T?)
 class Java {
     internal fun test() {

nj2k/testData/newJ2k/issues/kt-6790.kt

@@ -1,5 +1,3 @@
-import kotlin.collections.Map.Entry
-
 class A {
-    internal fun foo(o: Entry<Any?, Any?>?) {}
+    internal fun foo(o: Map.Entry<Any?, Any?>?) {}
 }