JVM_IR: partially fix inline methods using captured crossinline lambdas

The fields containing crossinline lambdas should be package-private to
avoid generating synthetic accessors, which break object regeneration.

Note that the inline methods cannot actually be called, as call sites
will attempt to read the captured lambda from a field through a *copy*
of the local containing the object, so these reads will not be inlined,
causing an exception at runtime:

    inline fun f(crossinline g: () -> Unit) = object : I {
        inline fun h() = g()
        // effectively `val tmp = this; return tmp.$g()`:
        override fun run() = h()
    }

    f {}.run() // NoSuchFieldError: $g

This particular example can be fixed by reusing locals for receiver
parameters in IrInlineCodegen, but explicitly assigning `this` to
another variable and calling an inline method on it will break it again.
(This is only applicable to the JVM_IR backend, as the non-IR one fails
to generate `f` at all for some other reason.)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/LocalDeclarationsLowering.kt

@@ -66,6 +66,9 @@ interface VisibilityPolicy {
     fun forConstructor(declaration: IrConstructor, inInlineFunctionScope: Boolean): Visibility =
         Visibilities.PRIVATE
 
+    fun forCapturedField(value: IrValueSymbol): Visibility =
+        Visibilities.PRIVATE
+
     companion object {
         val DEFAULT = object : VisibilityPolicy {}
     }
@@ -778,7 +781,7 @@ class LocalDeclarationsLowering(
                     classDeclaration.startOffset,
                     classDeclaration.endOffset,
                     suggestNameForCapturedValue(owner, generatedNames),
-                    Visibilities.PRIVATE,
+                    visibilityPolicy.forCapturedField(capturedValue),
                     classDeclaration,
                     owner.type,
                     owner is IrValueParameter && owner.isCrossinline

compiler/ir/backend.jvm/src/org/jetbrains/kotlin/backend/jvm/JvmLower.kt

@@ -11,12 +11,13 @@ import org.jetbrains.kotlin.backend.common.lower.*
 import org.jetbrains.kotlin.backend.common.lower.loops.forLoopsPhase
 import org.jetbrains.kotlin.backend.common.lower.optimizations.foldConstantLoweringPhase
 import org.jetbrains.kotlin.backend.common.phaser.*
-import org.jetbrains.kotlin.backend.jvm.ir.getJvmVisibilityOfDefaultArgumentStub
 import org.jetbrains.kotlin.backend.jvm.lower.*
 import org.jetbrains.kotlin.descriptors.Visibilities
 import org.jetbrains.kotlin.descriptors.Visibility
 import org.jetbrains.kotlin.ir.IrElement
 import org.jetbrains.kotlin.ir.declarations.*
+import org.jetbrains.kotlin.ir.symbols.IrValueParameterSymbol
+import org.jetbrains.kotlin.ir.symbols.IrValueSymbol
 import org.jetbrains.kotlin.ir.util.PatchDeclarationParentsVisitor
 import org.jetbrains.kotlin.ir.util.isAnonymousObject
 import org.jetbrains.kotlin.ir.util.parentAsClass
@@ -129,6 +130,12 @@ internal val localDeclarationsPhase = makeIrFilePhase<CommonBackendContext>(
                     else
                         declaration.visibility
 
+                override fun forCapturedField(value: IrValueSymbol): Visibility =
+                    if (value is IrValueParameterSymbol && value.owner.isCrossinline)
+                        JavaVisibilities.PACKAGE_VISIBILITY // avoid requiring a synthetic accessor for it
+                    else
+                        Visibilities.PRIVATE
+
                 private fun scopedVisibility(inInlineFunctionScope: Boolean): Visibility =
                     if (inInlineFunctionScope) Visibilities.PUBLIC else JavaVisibilities.PACKAGE_VISIBILITY
             }