FIR Java: add nullable (instead of not-null) type parameter bounds

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/JavaSymbolProvider.kt

@@ -136,7 +136,7 @@ class JavaSymbolProvider(
     ) {
         require(this is FirTypeParameterImpl)
         for (upperBound in javaTypeParameter.upperBounds) {
-            bounds += upperBound.toFirResolvedTypeRef(this@JavaSymbolProvider.session, stack)
+            bounds += upperBound.toFirResolvedTypeRef(this@JavaSymbolProvider.session, stack, isNullable = true)
         }
         addDefaultBoundIfNecessary()
     }

compiler/fir/java/src/org/jetbrains/kotlin/fir/java/JavaUtils.kt

@@ -93,9 +93,9 @@ internal fun JavaType.toFirJavaTypeRef(session: FirSession, javaTypeParameterSta
 }
 
 internal fun JavaClassifierType.toFirResolvedTypeRef(
-    session: FirSession, javaTypeParameterStack: JavaTypeParameterStack
+    session: FirSession, javaTypeParameterStack: JavaTypeParameterStack, isNullable: Boolean = false
 ): FirResolvedTypeRef {
-    val coneType = this.toConeKotlinTypeWithNullability(session, javaTypeParameterStack, isNullable = false)
+    val coneType = this.toConeKotlinTypeWithNullability(session, javaTypeParameterStack, isNullable)
     return FirResolvedTypeRefImpl(
         source = null, type = coneType
     ).apply {