Move VideoEncoderConfig from api/ into video/config

This cl move VideoEncoderConfig from api/ to video/config.

VideoStreamEncoderInterface and VideoStreamEncoderObserver
are moved as collateral.

brandt@ think that the reason these were in api/ in the
first place had to downstream project.

Functionality wise, this is a NOP, but it makes it easier
to modify the encoder (config).

Bug: webrtc:14451
Change-Id: I2610d815aeb186298498e7102cac773ecac8cd36
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/277002
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Reviewed-by: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#38242}
diff --git a/rtc_tools/BUILD.gn b/rtc_tools/BUILD.gn
index 9cf7790..9e6dd0f 100644
--- a/rtc_tools/BUILD.gn
+++ b/rtc_tools/BUILD.gn
@@ -218,6 +218,7 @@
       "../test:fileutils",
       "../test:rtp_test_utils",
       "../test:video_test_common",
+      "../video/config:encoder_config",
       "../video/config:streams_config",
       "//third_party/abseil-cpp/absl/flags:flag",
       "//third_party/abseil-cpp/absl/flags:parse",