[iOS] Move InterfaceProvider header to a separate target.

Some code (e.g. an app agent in follow-up CL) will require this header;
split it into a separate target to prevent circular deps.

Bug: none
Change-Id: I3c6c57f6e29bbf8c7156d30b71ba08681b2ecc93
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521124Reviewed-by: Mark Cogan <marq@chromium.org>
Commit-Queue: Stepan Khapugin <stkhapugin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826832}

ios/chrome/browser/ui/main/BUILD.gn

@@ -138,10 +138,16 @@ source_set("scene") {
   frameworks = [ "UIKit.framework" ]
 }
 
+source_set("browser_interface_provider") {
+  configs += [ "//build/config/compiler:enable_arc" ]
+  sources = [ "browser_interface_provider.h" ]
+  deps = [ "//base" ]
+  frameworks = [ "UIKit.framework" ]
+}
+
 source_set("main") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
-    "browser_interface_provider.h",
     "browser_view_wrangler.h",
     "browser_view_wrangler.mm",
     "bvc_container_view_controller.h",
@@ -202,7 +208,10 @@ source_set("main") {
     deps += [ "//ios/chrome/app/resources:base_scene_storyboard" ]
   }
 
-  public_deps = [ ":scene_state_header" ]
+  public_deps = [
+    ":browser_interface_provider",
+    ":scene_state_header",
+  ]
 
   # TODO(crbug.com/1103553): remove circular dependency.
   allow_circular_includes_from = [ "//ios/chrome/browser/ui/settings/sync" ]