FIR: Fix inference case with flexible captured types

Previsously, errors have been ignored because we ignored errors raised
from the completion phase

See the comment above the createConstraintPartForLowerBoundAndFlexibleTypeVariable

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

@@ -7,7 +7,6 @@ package org.jetbrains.kotlin.types.model
 
 import org.jetbrains.kotlin.types.AbstractTypeCheckerContext
 import org.jetbrains.kotlin.types.Variance
-import kotlin.collections.ArrayList
 import kotlin.contracts.ExperimentalContracts
 import kotlin.contracts.contract
 
@@ -238,6 +237,17 @@ interface TypeSystemInferenceExtensionContext : TypeSystemContext, TypeSystemBui
 
     @OptIn(ExperimentalStdlibApi::class)
     fun KotlinTypeMarker.extractTypeVariables() = buildSet { extractTypeVariables(this) }
+
+    /**
+     * For case Foo <: (T..T?) return LowerBound for new constraint LowerBound <: T
+     * In FE 1.0, in case nullable it was just Foo?, so constraint was Foo? <: T
+     * But it's not 100% correct because prevent having not-nullable upper constraint on T while initial (Foo? <: (T..T?)) is not violated
+     *
+     * In FIR, we try to have a correct one: (Foo!!..Foo?) <: T
+     *
+     * In future once we have only FIR (or FE 1.0 behavior is fixed) this method should be inlined to the use-site
+     */
+    fun SimpleTypeMarker.createConstraintPartForLowerBoundAndFlexibleTypeVariable(): KotlinTypeMarker
 }