[FIR/NI] Refactor type variable gathering from lambda types

Motivation:
- drop getArguments from type context as a duplicate of getArgumentList
- reduce the number of collection allocations in getAllDeeplyRelatedTypeVariables

Additional minor improvements, test data fixes

core/compiler.common/src/org/jetbrains/kotlin/types/model/TypeSystemContext.kt

@@ -246,7 +246,6 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
 
     fun KotlinTypeMarker.argumentsCount(): Int
     fun KotlinTypeMarker.getArgument(index: Int): TypeArgumentMarker
-    fun KotlinTypeMarker.getArguments(): List<TypeArgumentMarker>
 
     fun SimpleTypeMarker.getArgumentOrNull(index: Int): TypeArgumentMarker? {
         if (index in 0 until argumentsCount()) return getArgument(index)
@@ -341,6 +340,18 @@ interface TypeSystemContext : TypeSystemOptimizationContext {
         }
     }
 
+    operator fun TypeArgumentListMarker.iterator() = object : Iterator<TypeArgumentMarker> {
+        private var argumentIndex: Int = 0
+
+        override fun hasNext(): Boolean = argumentIndex < size()
+
+        override fun next(): TypeArgumentMarker {
+            val argument = get(argumentIndex)
+            argumentIndex += 1
+            return argument
+        }
+    }
+
     fun TypeConstructorMarker.isAnyConstructor(): Boolean
     fun TypeConstructorMarker.isNothingConstructor(): Boolean