Move accessibility component extensions into shared accessibility/ directory

As part of a transition to share code and tooling more easily between
ChromeVox, Switch Access, Select-to-Speak, autoclick, and any future
accessibility component extensions, move them into a shared
accessibility/ directory in chrome/browser/resources/chromeos.

Bug: 706981
Change-Id: Icaec4981380ac37e42d12706c2ec5693f58c334c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1913122
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#717744}

diff --git a/BUILD.gn b/BUILD.gn
index eb890e45..4cff2f26 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -653,7 +653,7 @@
   if (is_chromecast) {
     deps += [ "//chromecast:cast_shell" ]
     if (enable_extensions && use_aura) {
-      deps += [ "//chrome/browser/resources/chromeos/chromevox" ]
+      deps += [ "//chrome/browser/resources/chromeos/accessibility/chromevox" ]
     }
   }