fix: add reflections configs for generated firestore classes

[mpeddada1]

For tests failing in #1417.
Stacktrace:

  JUnit Vintage:ITSystemTest:testBuildingBundleWhenDocumentDoesNotExist
    MethodSource [className = 'com.google.cloud.firestore.it.ITSystemTest', methodName = 'testBuildingBundleWhenDocumentDoesNotExist', methodParameterTypes = '']
    => java.lang.IllegalStateException: Generated message class "com.google.firestore.bundle.BundleElement" missing method "getMetadata".
       com.google.protobuf.GeneratedMessageV3.getMethodOrDie(GeneratedMessageV3.java:1998)
       com.google.protobuf.GeneratedMessageV3.access$1000(GeneratedMessageV3.java:79)
       com.google.protobuf.GeneratedMessageV3$FieldAccessorTable$SingularFieldAccessor$ReflectionInvoker.<init>(GeneratedMessageV3.java:2347)
       com.google.protobuf.GeneratedMessageV3$FieldAccessorTable$SingularFieldAccessor.<init>(GeneratedMessageV3.java:2418)
       com.google.protobuf.GeneratedMessageV3$FieldAccessorTable$SingularMessageFieldAccessor.<init>(GeneratedMessageV3.java:3105)
       [...]
     Caused by: java.lang.NoSuchMethodException: com.google.firestore.bundle.BundleElement.getMetadata()
       java.base@11.0.19/java.lang.Class.getMethod(DynamicHub.java:2108)
       com.google.protobuf.GeneratedMessageV3.getMethodOrDie(GeneratedMessageV3.java:1995)
       [...]

Using IntelliJ debugger, it can be determined that FirestoreBundle#elementToLengthPrefixedStringBuilder invokes JsonFormat$Printer#print which transitively invokes GeneratedMessagev3#getMethodOrDie that reflectively calls methods in com.google.firestore.bundle.BundleElement, com.google.firestore.bundle.BundleMetadata and so on.

[suztomo]

As long as the GraalVM test passes, it's good.