Adding default_exe_manifest to some gn binaries

gn builds are missing Windows manifests for some webrtc executables.
These manifests are necessary in order to get predictable behavior on
Windows.

BUG=602505
NOTRY=True

Review-Url: https://codereview.webrtc.org/1927793002
Cr-Original-Commit-Position: refs/heads/master@{#12540}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 84583e03c7b7198d9c311d49523563b5e68274a2