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