--sub-ass-style-overrides for srt subs

[korongmambu]

Since srt subs also can change font color with tag in the script, it will be fair if mpv can override those srt subs like ass subs does with --sub-ass-style-overrides, so it can override without needed to set --sub-ass-override=strip, either with new option like --sub-srt-style-overrides or just let --sub-ass-style-overrides handle it