webrtc: sendonly: Add support for Windows

Add meson build script and use mfvideosrc element in case of Windows

Part-of: <!29>
25 jobs for master in 33 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build Docker
passed #6095133
alpine amd64 manifest builder docker

00:00:17

passed #6095132
android docker

00:00:17

passed #6095131
cerbero fedora amd64 docker

00:00:21

passed #6095130
fedora amd64 docker

00:00:15

passed #6095134
gst-indent amd64 docker

00:00:18

 
  Preparation
passed #6095136
gst indent

00:00:11

manual #6095135
manual
manifest
 
  Build
created #6095145
gstreamer
build cerbero cross-android universal
created #6095149
gst-ios-13.2
build cerbero cross-ios universal
created #6095146
gstreamer
build cerbero cross win32
created #6095147
gstreamer
build cerbero cross win64
created #6095144
gstreamer
build cerbero fedora x86_64
created #6095148
gst-macos-10.15
build cerbero macos x86_64
created #6095150
docker windows gstreamer-windows 1809
build cerbero msvc x86_64
created #6095140
build clang fedora x86_64
created #6095143
docker windows 1809 allowed to fail manual
build msys2
created #6095137
build nodebug fedora x86_64
created #6095138
build static fedora x86_64
created #6095139
build static nodebug fedora x86_64
created #6095141
docker windows 1809
build vs2017 amd64
created #6095142
docker windows 1809
build vs2017 x86
 
  Test
created #6095151
gstreamer
check fedora
 
  Integrate
created #6095152
cross-android universal examples
created #6095154
gst-ios-13.2
cross-ios universal examples
created #6095153
documentation