fate/subtitles: Add a new test for WebVTT

Includes escapes that should now be supported and a few features not yet
fully supported, like comments, regions, classes, ruby, and lang.

All were tested with https://quuz.org/webvtt/ for validation, except
regions because the validator doesn't support them yet, and I couldn't
find any other way to validate WebVTT.
Signed-off-by: Ricardo Constantino <wiiaboo@gmail.com>

tests/fate/subtitles.mak

@@ -70,6 +70,9 @@ fate-sub-vplayer: CMD = fmtstdout ass -i $(TARGET_SAMPLES)/sub/VPlayer_capabilit
 FATE_SUBTITLES_ASS-$(call DEMDEC, WEBVTT, WEBVTT) += fate-sub-webvtt
 fate-sub-webvtt: CMD = fmtstdout ass -i $(TARGET_SAMPLES)/sub/WebVTT_capability_tester.vtt
 
+FATE_SUBTITLES_ASS-$(call DEMDEC, WEBVTT, WEBVTT) += fate-sub-webvtt2
+fate-sub-webvtt2: CMD = fmtstdout ass -i $(TARGET_SAMPLES)/sub/WebVTT_extended_tester.vtt
+
 FATE_SUBTITLES-$(call ALLYES, SRT_DEMUXER SUBRIP_DECODER WEBVTT_ENCODER WEBVTT_MUXER) += fate-sub-webvttenc
 fate-sub-webvttenc: CMD = fmtstdout webvtt -i $(TARGET_SAMPLES)/sub/SubRip_capability_tester.srt
 

tests/ref/fate/sub-webvtt2

+[Script Info]
+; Script generated by FFmpeg/Lavc
+ScriptType: v4.00+
+PlayResX: 384
+PlayResY: 288
+
+[V4+ Styles]
+Format: Name, Fontname, Fontsize, PrimaryColour, SecondaryColour, OutlineColour, BackColour, Bold, Italic, Underline, StrikeOut, ScaleX, ScaleY, Spacing, Angle, BorderStyle, Outline, Shadow, Alignment, MarginL, MarginR, MarginV, Encoding
+Style: Default,Arial,16,&Hffffff,&Hffffff,&H0,&H0,0,0,0,0,100,100,0,0,1,1,0,2,10,10,10,0
+
+[Events]
+Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
+Dialogue: 0,0:00:00.00,0:00:20.00,Default,,0,0,0,,Hi, my name is Fred
+Dialogue: 0,0:00:02.50,0:00:22.50,Default,,0,0,0,,Hi, I’m Bill
+Dialogue: 0,0:00:05.00,0:00:25.00,Default,,0,0,0,,Would you like to get a coffee?
+Dialogue: 0,0:00:07.50,0:00:27.50,Default,,0,0,0,,Sure! I’ve only had one today.
+Dialogue: 0,0:00:10.00,0:00:30.00,Default,,0,0,0,,This is my fourth!
+Dialogue: 0,0:00:12.50,0:00:32.50,Default,,0,0,0,,OK, let’s go.
+Dialogue: 0,0:00:38.00,0:00:43.00,Default,,0,0,0,,I want to 愛あい love you\NThat's not proper English!
+Dialogue: 0,0:00:43.00,0:00:46.00,Default,,0,0,0,,{\i1}キツネ{\i0}じゃない　キツネじゃない\N乙女おとめは
+Dialogue: 0,0:00:50.00,0:00:55.00,Default,,0,0,0,,Some time ago in a rather distant place....
+Dialogue: 0,0:00:55.00,0:01:00.00,Default,,0,0,0,,Descending: 123456\NAscending: 123456
+Dialogue: 0,0:01:00.00,0:01:05.00,Default,,0,0,0,,>> Never gonna give you up Never gonna let you down\NNever\hgonna\hrun\haround & desert\hyou