[CrOS Cellular] Add Hermes Euicc dbus client.

The hermes DBus API is is changing in https://crrev.com/c/2276588.
This change essentially moves all methods from the manager interface
into a new Euicc interface. Each Euicc object corresponds to an euicc
hardware available on the device. The main manager object now simply
holds list of available euiccs.

Bug: 1093185
Change-Id: Ib0b668cf47a9b8c3fb3016847d59024492443d73
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303285
Commit-Queue: Azeem Arshad <azeemarshad@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#793249}

chromeos/dbus/hermes/BUILD.gn

@@ -21,6 +21,8 @@ source_set("hermes_clients") {
   sources = [
     "hermes_clients.cc",
     "hermes_clients.h",
+    "hermes_euicc_client.cc",
+    "hermes_euicc_client.h",
     "hermes_manager_client.cc",
     "hermes_manager_client.h",
     "hermes_profile_client.cc",
@@ -40,6 +42,8 @@ source_set("hermes_fakes") {
   ]
 
   sources = [
+    "fake_hermes_euicc_client.cc",
+    "fake_hermes_euicc_client.h",
     "fake_hermes_manager_client.cc",
     "fake_hermes_manager_client.h",
     "fake_hermes_profile_client.cc",
@@ -64,7 +68,7 @@ source_set("test_support") {
   sources = [
     "hermes_client_test_base.cc",
     "hermes_client_test_base.h",
-    "hermes_manager_client_unittest.cc",
+    "hermes_euicc_client_unittest.cc",
     "hermes_profile_client_unittest.cc",
     "hermes_test_utils.cc",
     "hermes_test_utils.h",