[build] Add cppgc_headers dep to v8_headers

To fix 6 gn check errors, this adds a cppgc_headers dep to v8_headers.
To resolve the resulting cycle, it also changes v8_libplatform to depend
on v8_config_headers since it only needs v8config.h.

Bug: v8:7330
Change-Id: I1e21271c84f2a80c248c584e8e107da99eaad5a9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2727500
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73120}

BUILD.gn

@@ -2131,7 +2131,10 @@ v8_header_set("v8_headers") {
 
   public_deps = [ ":v8_config_headers" ]
 
-  deps = [ ":v8_version" ]
+  deps = [
+    ":cppgc_headers",
+    ":v8_version",
+  ]
 }
 
 if (v8_generate_external_defines_header) {
@@ -4650,7 +4653,7 @@ v8_component("v8_libplatform") {
   public_deps = []
 
   deps = [
-    ":v8_headers",
+    ":v8_config_headers",
     ":v8_libbase",
     ":v8_tracing",
   ]