devops: fine-tune ffmpeg compilation (microsoft#3823)

This patch:
- removes `--enable-gpl` and `--enable-version3` flags. This defaults
builds to LGPL2 license
- includes `--disable-autodetect` to ensure determenism
- includes extra version suffix to link from binary files back to these
build scripts

Author: aslushnikov

browser_patches/ffmpeg/BUILD_NUMBER

@@ -1 +1 @@
-1000
+1001

browser_patches/ffmpeg/CONFIG.sh

@@ -21,9 +21,9 @@ LIBVPX_CONFIG="--enable-static \
                --disable-examples"
 
 FFMPEG_VERSION="n4.3.1"
-FFMPEG_CONFIG="--enable-gpl \
-               --enable-version3 \
+FFMPEG_CONFIG="--extra-version=playwright-build-$(cat ./BUILD_NUMBER | head -1) \
                --disable-debug \
+               --disable-autodetect \
                --disable-everything \
                --enable-ffmpeg \
                --enable-protocol=pipe \