Split most core build rules into various BUILD.gn files in core.

Change-Id: I773eec2bbf104f073eba7a64ed19f6fba0131d21
Reviewed-on: https://pdfium-review.googlesource.com/c/43946
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Henrique Nakashima <hnakashima@chromium.org>
diff --git a/fxbarcode/BUILD.gn b/fxbarcode/BUILD.gn
index 88235be..524ca7b 100644
--- a/fxbarcode/BUILD.gn
+++ b/fxbarcode/BUILD.gn
@@ -136,7 +136,7 @@
   ]
   deps = [
     "../:fxcrt",
-    "../:fxge",
+    "../core/fxge",
     "../third_party:bigint",
   ]
   configs += [ "../:pdfium_core_config" ]