Move credential_manager.mojom to third_party/blink/public/mojom/

This change moves credential_manager.mojom to
third_party/blink/public/mojom. This allows making a follow-up change
where document_interface_broker.mojom depends on credential_manager.mojom
without creating a circular dependency:
//third_party/blink/public:mojo_bindings ->
//third_party/blink/public/mojom:mojom_platform
(document_interface_broker) ->
//third_party/blink/public:mojo_bindings
(credential_manager).

Also there is a # TODO: Move these into blink/public/mojom.

Bug: 936482

Change-Id: Ia160559a665d74a77a1b20b506812b6b7c6536b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1525013
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Oksana Zhuravlova <oksamyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641503}
19 files changed