command: use scale_units to add/cycle integer properties

This adds check_property_scalable, which returns true if the property is
backed by a floating-point number. When the add or cycle commands
operate on these properties, they can benefit from the fractional scale
value in cmd->scale. When the property is not backed by a floating-point
number, cmd->scale_units is used instead, so for axis events, the
property is only incrmented when the user scrolls one full unit.

This solution isn't perfect, because in some cases integer-backed
properties could benefit from accurate scrolling. For example, if an
axis is bound to "cycle audio 5", the cycle command could be made to
change the audio track by one when the user scrolls 1/5th of a unit,
though this behaviour would require more changes to the options system.

input/cmd_parse.c

@@ -140,7 +140,7 @@ struct mp_cmd *mp_input_parse_cmd_node(struct mp_log *log, mpv_node *node)
 {
     struct mp_cmd *cmd = talloc_ptrtype(NULL, cmd);
     talloc_set_destructor(cmd, destroy_cmd);
-    *cmd = (struct mp_cmd) { .scale = 1, };
+    *cmd = (struct mp_cmd) { .scale = 1, .scale_units = 1 };
 
     if (node->format != MPV_FORMAT_NODE_ARRAY)
         goto error;
@@ -254,6 +254,7 @@ static struct mp_cmd *parse_cmd_str(struct mp_log *log, void *tmp,
     *cmd = (struct mp_cmd) {
         .flags = MP_ON_OSD_AUTO | MP_EXPAND_PROPERTIES,
         .scale = 1,
+        .scale_units = 1,
     };
 
     ctx->str = bstr_lstrip(ctx->str);

input/input.c

@@ -618,11 +618,13 @@ static void interpret_key(struct input_ctx *ictx, int code, double scale,
 
     if (mp_input_is_scalable_cmd(cmd)) {
         cmd->scale = scale;
+        cmd->scale_units = scale_units;
         mp_input_queue_cmd(ictx, cmd);
     } else {
         // Non-scalable commands won't understand cmd->scale, so synthesize
         // multiple commands with cmd->scale = 1
         cmd->scale = 1;
+        cmd->scale_units = 1;
         // Avoid spamming the player with too many commands
         scale_units = FFMIN(scale_units, 20);
         for (int i = 0; i < scale_units - 1; i++)

input/input.h

@@ -85,6 +85,7 @@ typedef struct mp_cmd {
     int mouse_x, mouse_y;
     struct mp_cmd *queue_next;
     double scale;               // for scaling numeric arguments
+    int scale_units;
     const struct mp_cmd_def *def;
     char *sender; // name of the client API user which sent this
     char *key_name; // string representation of the key binding