[FIR] Move ReturnTypeCalculator to :fir:providers module

Also make it an abstract class and turn ReturnTypeCalculatorForFullBodyResolve
  into object (because it has no state and there is no need to create
  different instances of it)

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/collectors/SimpleDiagnosticsCollector.kt

@@ -21,7 +21,7 @@ class SimpleDiagnosticsCollector(
         return CheckerRunningDiagnosticCollectorVisitor(
             MutableCheckerContext(
                 this,
-                ReturnTypeCalculatorForFullBodyResolve()
+                ReturnTypeCalculatorForFullBodyResolve
             ),
             components
         )

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/transformers/ReturnTypeCalculator.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2022 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.
  */
 
@@ -9,8 +9,8 @@ import org.jetbrains.kotlin.fir.declarations.FirTypedDeclaration
 import org.jetbrains.kotlin.fir.symbols.impl.FirCallableSymbol
 import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
 
-interface ReturnTypeCalculator {
+abstract class ReturnTypeCalculator {
-    fun tryCalculateReturnType(declaration: FirTypedDeclaration): FirResolvedTypeRef
+    abstract fun tryCalculateReturnType(declaration: FirTypedDeclaration): FirResolvedTypeRef
 
     fun tryCalculateReturnType(symbol: FirCallableSymbol<*>): FirResolvedTypeRef {
         return tryCalculateReturnType(symbol.fir)

compiler/fir/providers/src/org/jetbrains/kotlin/fir/resolve/transformers/ReturnTypeCalculatorForFullBodyResolve.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2021 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2022 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.
  */
 
@@ -13,7 +13,7 @@ import org.jetbrains.kotlin.fir.scopes.FakeOverrideTypeCalculator
 import org.jetbrains.kotlin.fir.types.FirResolvedTypeRef
 import org.jetbrains.kotlin.fir.types.builder.buildErrorTypeRef
 
-class ReturnTypeCalculatorForFullBodyResolve : ReturnTypeCalculator {
+object ReturnTypeCalculatorForFullBodyResolve : ReturnTypeCalculator() {
     override fun tryCalculateReturnType(declaration: FirTypedDeclaration): FirResolvedTypeRef {
         val returnTypeRef = declaration.returnTypeRef
         if (returnTypeRef is FirResolvedTypeRef) return returnTypeRef

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirBodyResolveTransformer.kt

@@ -20,7 +20,6 @@ import org.jetbrains.kotlin.fir.resolve.transformers.FirProviderInterceptor
 import org.jetbrains.kotlin.fir.resolve.transformers.ReturnTypeCalculator
 import org.jetbrains.kotlin.fir.resolve.transformers.ReturnTypeCalculatorForFullBodyResolve
 import org.jetbrains.kotlin.fir.resolve.transformers.ScopeClassDeclaration
-import org.jetbrains.kotlin.fir.scopes.FirCompositeScope
 import org.jetbrains.kotlin.fir.types.*
 import org.jetbrains.kotlin.fir.visitors.FirTransformer
 
@@ -29,7 +28,7 @@ open class FirBodyResolveTransformer(
     phase: FirResolvePhase,
     override var implicitTypeOnly: Boolean,
     scopeSession: ScopeSession,
-    val returnTypeCalculator: ReturnTypeCalculator = ReturnTypeCalculatorForFullBodyResolve(),
+    val returnTypeCalculator: ReturnTypeCalculator = ReturnTypeCalculatorForFullBodyResolve,
     outerBodyResolveContext: BodyResolveContext? = null,
     val firTowerDataContextCollector: FirTowerDataContextCollector? = null,
     val firProviderInterceptor: FirProviderInterceptor? = null,

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirImplicitBodyResolve.kt

@@ -204,7 +204,7 @@ private class ReturnTypeCalculatorWithJump(
         returnTypeCalculator: ReturnTypeCalculator,
         outerBodyResolveContext: BodyResolveContext?
     ) -> FirDesignatedBodyResolveTransformerForReturnTypeCalculator = ::FirDesignatedBodyResolveTransformerForReturnTypeCalculator,
-) : ReturnTypeCalculator {
+) : ReturnTypeCalculator() {
 
     @OptIn(PrivateForInline::class)
     var outerBodyResolveContext: BodyResolveContext? = null

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/contracts/FirContractResolveTransformerAdapter.kt

@@ -42,7 +42,7 @@ fun <F : FirClassLikeDeclaration> F.runContractResolveForLocalClass(
     targetedClasses: Set<FirClassLikeDeclaration>
 ): F {
     val newContext = outerBodyResolveContext.createSnapshotForLocalClasses(
-        ReturnTypeCalculatorForFullBodyResolve(),
+        ReturnTypeCalculatorForFullBodyResolve,
         targetedClasses
     )
     val transformer = FirContractResolveTransformer(session, scopeSession, newContext)