Update v8 version to 8.4

TBR=liviurau@chromium.org,machenbach@chromium.org
NOTRY=true

Change-Id: I05c093c22d9d5d6ac889a8229bee5b23e12d6f1e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2134370Reviewed-by: Lutz Vahl <vahl@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Liviu Rau <liviurau@chromium.org>
Reviewed-by: Michael Hablich <hablich@chromium.org>
Commit-Queue: Lutz Vahl <vahl@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66968}

include/v8-version.h

@@ -9,7 +9,7 @@
 // NOTE these macros are used by some of the tool scripts and the build
 // system so their names cannot be changed without changing the scripts.
 #define V8_MAJOR_VERSION 8
-#define V8_MINOR_VERSION 3
+#define V8_MINOR_VERSION 4
 #define V8_BUILD_NUMBER 0
 #define V8_PATCH_LEVEL 0