Introduce frontend independent constraint positions

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/calls/CreateFreshTypeVariableSubstitutorStage.kt

@@ -17,7 +17,7 @@ import org.jetbrains.kotlin.fir.symbols.impl.FirTypeParameterSymbol
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.types.impl.FirTypePlaceholderProjection
 import org.jetbrains.kotlin.resolve.calls.inference.ConstraintSystemOperation
-import org.jetbrains.kotlin.resolve.calls.inference.model.FirDeclaredUpperBoundConstraintPosition
+import org.jetbrains.kotlin.fir.resolve.inference.model.FirDeclaredUpperBoundConstraintPosition
 import org.jetbrains.kotlin.resolve.calls.inference.model.SimpleConstraintSystemConstraintPosition
 
 internal object CreateFreshTypeVariableSubstitutorStage : ResolutionStage() {

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/FirBuilderInferenceSession.kt

@@ -190,7 +190,7 @@ class FirBuilderInferenceSession(
             for ((variableConstructor, type) in storage.fixedTypeVariables) {
                 val typeVariable = storage.allTypeVariables.getValue(variableConstructor)
                 commonSystem.registerVariable(typeVariable)
-                commonSystem.addEqualityConstraint((typeVariable as ConeTypeVariable).defaultType, type, CoroutinePosition())
+                commonSystem.addEqualityConstraint((typeVariable as ConeTypeVariable).defaultType, type, CoroutinePosition)
                 introducedConstraint = true
             }
         }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/PostponedArgumentsAnalyzer.kt

@@ -142,7 +142,7 @@ class PostponedArgumentsAnalyzer(
                     val variable = variableWithConstraints.typeVariable as ConeTypeVariable
 
                     c.getBuilder().unmarkPostponedVariable(variable)
-                    c.getBuilder().addEqualityConstraint(variable.defaultType, resultType, CoroutinePosition())
+                    c.getBuilder().addEqualityConstraint(variable.defaultType, resultType, CoroutinePosition)
                 }
             }
         }

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/inference/model/FirConstraintPositionAndErrors.kt

@@ -0,0 +1,10 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.fir.resolve.inference.model
+
+import org.jetbrains.kotlin.resolve.calls.inference.model.DeclaredUpperBoundConstraintPosition
+
+class FirDeclaredUpperBoundConstraintPosition : DeclaredUpperBoundConstraintPosition<Nothing?>(null)