Mark classes with final dtors as final

- -Wfinal-dtor-non-final-class warns on classes with final dtors but
  not final classes.
- Error messages are better when the class is marked final.
- Fix existing issues in code base and remove warning exemption

Bug: chromium:999886
Test: no errors building
Change-Id: Ied2a7a2ff890ecbaf0a4c84f5323f0c9d32def58
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2467000Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70509}

src/parsing/scanner-character-streams.cc

@@ -331,7 +331,7 @@ class UnbufferedCharacterStream : public Utf16CharacterStream {
 
 // Provides a unbuffered utf-16 view on the bytes from the underlying
 // ByteStream.
-class RelocatingCharacterStream
+class RelocatingCharacterStream final
     : public UnbufferedCharacterStream<OnHeapStream> {
  public:
   template <class... TArgs>
@@ -422,7 +422,7 @@ bool BufferedUtf16CharacterStream::ReadBlock() {
 // TODO(verwaest): Decode utf8 chunks into utf16 chunks on the blink side
 // instead so we don't need to buffer.
 
-class Utf8ExternalStreamingStream : public BufferedUtf16CharacterStream {
+class Utf8ExternalStreamingStream final : public BufferedUtf16CharacterStream {
  public:
   Utf8ExternalStreamingStream(
       ScriptCompiler::ExternalSourceStream* source_stream)