FIR: split default importing scopes into low/high priority ones

This fixes resolve of StringBuilder(), AssertionError(), etc.

compiler/testData/ir/irText/expressions/kt30796.fir.txt

@@ -4,7 +4,7 @@ FILE fqName:<root> fileName:/kt30796.kt
     BLOCK_BODY
       RETURN type=kotlin.Nothing from='public final fun magic <T> (): T of <root>.magic declared in <root>'
         THROW type=kotlin.Nothing
-          ERROR_CALL 'Unresolved reference: <Ambiguity: Exception, [java/lang/Exception.Exception, java/lang/Exception.Exception]>#' type=IrErrorType
+          CONSTRUCTOR_CALL 'public constructor <init> () declared in java.lang.Exception' type=java.lang.Exception origin=null
   FUN name:test visibility:public modality:FINAL <T> (value:T of <root>.test, value2:T of <root>.test) returnType:kotlin.Unit
     TYPE_PARAMETER name:T index:0 variance: superTypes:[]
     VALUE_PARAMETER name:value index:0 type:T of <root>.test