config: change default grapheme-width-method from wcswidth to double-width

The old default, wcswidth, simply calls wcswidth() on the grapheme
cluster. This was supposedly the implementation with the highest
application compatibility. Except we never even tried to measure
it. It was just assumed.

A lot of modern applications have better implementations. Let’s try to
push support for better emoji support by changing our default method
from wcswith to double-width.

While far from correct (it’s not based on the Unicode tables), the
‘double-width’ method produces accurate results anyway.

double-width is like wcswidth(), in that it adds together the
individual wcwidths of all codepoints in the grapheme cluster. But, it
limits the maximum width to 2.

CHANGELOG.md

@@ -75,6 +75,7 @@
 * Set `PWD` environment variable in the slave process ([#1179][1179]).
 * DPI is now forced to 96 when found to be unreasonably high.
 * Set default log level to warning ([#1215][1215]).
+* Default `grapheme-width-method` from `wcswidth` to `double-width`.
 
 [1166]: https://codeberg.org/dnkl/foot/issues/1166
 [1179]: https://codeberg.org/dnkl/foot/issues/1179

config.c

@@ -3003,7 +3003,7 @@ config_load(struct config *conf, const char *conf_path,
 #if defined(FOOT_GRAPHEME_CLUSTERING) && FOOT_GRAPHEME_CLUSTERING
             .grapheme_shaping = fcft_caps & FCFT_CAPABILITY_GRAPHEME_SHAPING,
 #endif
-            .grapheme_width_method = GRAPHEME_WIDTH_WCSWIDTH,
+            .grapheme_width_method = GRAPHEME_WIDTH_DOUBLE,
             .delayed_render_lower_ns = 500000,         /* 0.5ms */
             .delayed_render_upper_ns = 16666666 / 2,   /* half a frame period (60Hz) */
             .max_shm_pool_size = 512 * 1024 * 1024,

doc/foot.ini.5.scd

@@ -1256,7 +1256,7 @@ any of these options.
 	
 	*max* uses the width of the largest codepoint in the cluster.
 	
-	Default: _wcswidth_
+	Default: _double-width_
 
 *font-monospace-warn*
 	Boolean. When enabled, foot will use heuristics to try to verify