sub/sd_sbr: pass track language to sbr_load_text

The language hint is required for *correct* handling of RTL in srv3 so
provide the best-effort guess from the subtitle track.

Without this hint some RTL paragraphs are going to be wrongly assumed
LTR and reorder incorrectly. Additionally, subrandr may soon start
treating srv3 segments as `inline-block`s which means guessing is not
going to be possible anymore (at least as part of unicode bidi algorithm).

Author: afishhh

sub/dec_sub.c

@@ -75,6 +75,7 @@ struct dec_sub {
 
     struct mp_codec_params *codec;
     double start, end;
+    char *lang;
 
     double last_vo_pts;
     struct sd *sd;
@@ -171,6 +172,7 @@ static struct sd *init_decoder(struct dec_sub *sub)
             .order = sub->order,
             .attachments = sub->attachments,
             .codec = sub->codec,
+            .lang = sub->lang,
             .preload_ok = true,
         };
 
@@ -204,6 +206,7 @@ struct dec_sub *sub_create(struct mpv_global *global, struct track *track,
         .shared_opts_cache = m_config_cache_alloc(sub, global, &mp_subtitle_shared_sub_opts),
         .sh = track->stream,
         .codec = track->stream->codec,
+        .lang = track->lang,
         .attachments = talloc_steal(sub, attachments),
         .play_dir = 1,
         .order = order,

sub/sd.h

@@ -29,6 +29,7 @@ struct sd {
 
     struct attachment_list *attachments;
     struct mp_codec_params *codec;
+    const char *lang;
 
     // Set to false as soon as the decoder discards old subtitle events.
     // (only needed if sd_functions.accept_packets_in_advance == false)

sub/sd_sbr.c

@@ -148,7 +148,7 @@ static void decode(struct sd *sd, struct demux_packet *packet)
         packet->buffer,
         packet->len,
         fmt,
-        NULL
+        sd->lang
     );
 
     // Since `demux_sbr` only ever sends us one packet,