Move webrtc/{tools => rtc_tools}

Leaving compatibility script in webrtc/tools/compare_videos.py to
avoid breaking our video quality tests in Chromium.
Forwarding GN targets are left in webrtc/tools/BUILD.gn.

BUG=webrtc:7855
NOTRY=True
NOPRESUBMIT=True

Review-Url: https://codereview.webrtc.org/2965593002
Cr-Original-Commit-Position: refs/heads/master@{#18848}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d2b63cf1318e717e5acc4706409e79d824bb13c1
125 files changed