Add deskintl (desktop international) layout set.

Add a layout set aimed at desktop, laptop, and tablet devices with a larger
touchscreen. The layout is the US-International English, adding a compose key.
https://en.wikipedia.org/wiki/QWERTY#US-International

This layout set was created based on the layout set by the user nine7nine
(Jordan Johnston) <https://github.com/nine7nine>.

Note I copied the keymap.mobintl.h into the keymap.deskintl.h, and modified the
keymap.deskintl.h as follows to fix "<" (comma+shift), ">" (period+shift), "?"
(slash+shift) keys.

The following commit changed the key codes in the keymap.h for mobile. I
reverted the change for the keymap.deskintl.h.
9e4cf69137

Below is the difference between the keymap.mobintl.h and keymap.deskintl.h now.

```
$ diff -u keymap.mobintl.h keymap.deskintl.h
...
@@ -1226,9 +1225,9 @@
         key <AB05>               {	[               b,               B, equal ] };\
         key <AB06>               {	[               n,               N, question ] };\
         key <AB07>               {	[               m,               M, exclam ] };\
-        key <AB08>               {	[           comma,      apostrophe, less, U00AB] };\
-        key <AB09>               {	[          period,        question, greater, U00BB] };\
-        key <AB10>               {	[           slash,        greater ] };\
+        key <AB08>               {	[           comma,            less, backslash] };\
+        key <AB09>               {	[          period,         greater, bar ] };\
+        key <AB10>               {	[           slash,        question ] };\
         key <I147>               {  [      exclamdown,   questiondown, exclamdown ] };\
         key <RTSH>               {	[         Shift_R ] };\
         key <KPMU>               {\
...
```

Co-authored-by: Jordan Johnston <johnstonljordan@gmail.com>
Signed-off-by: Jun Aruga <jun.aruga@gmail.com>

config.deskintl.h

@@ -0,0 +1,45 @@
+#ifndef config_h_INCLUDED
+#define config_h_INCLUDED
+
+#define DEFAULT_FONT "Sans 14"
+#define DEFAULT_ROUNDING 5
+static const int transparency = 255;
+
+struct clr_scheme schemes[] = {
+{
+  /* colors */
+  .bg = {.bgra = {15, 15, 15, transparency}},
+  .fg = {.bgra = {45, 45, 45, transparency}},
+  .high = {.bgra = {100, 100, 100, transparency}},
+  .swipe = {.bgra = {100, 255, 100, 64}},
+  .text = {.color = UINT32_MAX},
+  .font = DEFAULT_FONT,
+  .rounding = DEFAULT_ROUNDING,
+},
+{
+  /* colors */
+  .bg = {.bgra = {15, 15, 15, transparency}},
+  .fg = {.bgra = {32, 32, 32, transparency}},
+  .high = {.bgra = {100, 100, 100, transparency}},
+  .swipe = {.bgra = {100, 255, 100, 64}},
+  .text = {.color = UINT32_MAX},
+  .font = DEFAULT_FONT,
+  .rounding = DEFAULT_ROUNDING,
+}
+};
+
+/* layers is an ordered list of layouts, used to cycle through */
+static enum layout_id layers[] = {
+  Full, // First layout is the default layout on startup
+  Special,
+  NumLayouts // signals the last item, may not be omitted
+};
+
+/* layers is an ordered list of layouts, used to cycle through */
+static enum layout_id landscape_layers[] = {
+  Full, // First layout is the default layout on startup
+  Special,
+  NumLayouts // signals the last item, may not be omitted
+};
+
+#endif // config_h_INCLUDED