Introduce TowerResolver.Task class

Its main purpose is code simplification: ImplicitScopeTower::run
contains a lot of local functions that are needed because of
lots of shared state

So, we're moving the state to the Task class instead

NB: This change doesn't change the code of `run`, it will be done
in further commits

compiler/resolution/src/org/jetbrains/kotlin/resolve/calls/tower/TowerResolver.kt

@@ -93,11 +93,21 @@ class TowerResolver {
     ): Collection<C>
             = scopeTower.run(processor, AllCandidatesCollector(), false, name)
 
+    fun <C : Candidate> ImplicitScopeTower.run(
+            processor: ScopeTowerProcessor<C>,
+            resultCollector: ResultCollector<C>,
+            useOrder: Boolean,
+            name: Name
+    ): Collection<C> = with(Task()) {
+        this@run.run(processor, resultCollector, useOrder, name)
+    }
+
     private data class ScopeLevelsAndSkippedForLookups(
             val levelsToProcess: Collection<ScopeTowerLevel>,
             val levelsToSkip: Collection<ScopeTowerLevel>
     )
 
+    private inner class Task {
         private fun ImplicitScopeTower.createNonLocalLevels(name: Name): ScopeLevelsAndSkippedForLookups {
             val mainResult = mutableListOf<ScopeTowerLevel>()
             val skippedLevels = mutableListOf<ScopeTowerLevel>()
@@ -138,7 +148,7 @@ class TowerResolver {
             return ScopeLevelsAndSkippedForLookups(mainResult, skippedLevels)
         }
 
-    private fun <C : Candidate> ImplicitScopeTower.run(
+        fun <C : Candidate> ImplicitScopeTower.run(
                 processor: ScopeTowerProcessor<C>,
                 resultCollector: ResultCollector<C>,
                 useOrder: Boolean,
@@ -253,6 +263,7 @@ class TowerResolver {
 
         private fun ResolutionScope.mayFitForName(name: Name) =
                 !definitelyDoesNotContainName(name) || !definitelyDoesNotContainName(OperatorNameConventions.INVOKE)
+    }
 
     fun <C : Candidate> runWithEmptyTowerData(
             processor: ScopeTowerProcessor<C>,