Reland "[Telemetry] Add implementation of Keyboard event"

This is a reland of commit 9efe89431b96a758bd7017b45fff1d12a3f364b8

Original change's description:
> [Telemetry] Add implementation of Keyboard event
>
> This change adds the actual implementation for the Keyboard
> diagnostic event.
>
> Bug: b/278670637
> Test: browser_tests --gtest_filter="*TelemetryExtensionEvents*"
> Change-Id: Ie252405d7a64986712a14d607c6f21d699b5cf28
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4537662
> Reviewed-by: Giovanni Ortuno Urquidi <ortuno@chromium.org>
> Reviewed-by: Oleh Lamzin <lamzin@google.com>
> Commit-Queue: Bastian Kersting <bkersting@google.com>
> Cr-Commit-Position: refs/heads/main@{#1148602}

Bug: b/278670637
Change-Id: Ica82774958be7e2965261886d4ea8c9e16331263
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4566603
Reviewed-by: Oleh Lamzin <lamzin@google.com>
Commit-Queue: Bastian Kersting <bkersting@google.com>
Cr-Commit-Position: refs/heads/main@{#1149663}