unicode: Support characters beyond the first unicode plane

We used 16-bit variables to store the 'character code' everywhere but
this won't let us represent anything beyond U+FFFF.

This patch changes those variables to a custom type that can be 32 or 16
bits depending on the build, and adjusts numerous internal APIs and
datastructures to match.  This includes:

 * utf8decode() and friends
 * font manipulation, caching, rendering, and generation
 * on-screen keyboard
 * FAT filesystem (parsing and generating utf16 LFNs)
 * WIN32 simulator platform code

Note that this patch doesn't _enable_ >16bit unicode support; a followup
patch will turn that on for appropriate targets.

Appears to work on:

  * hosted linux, native, linux simulator in both 16/32-bit modes.

Needs testing on:

  * windows and macos simulator (16bit+32bit)

Change-Id: Iba111b27d2433019b6bff937cf1ebd2c4353a0e8

tools/convbdf.c

@@ -116,7 +116,7 @@ int gen_h = 0;
 int gen_fnt = 0;
 int gen_map = 1;
 int start_char = 0;
-int limit_char = 65535;
+int limit_char = 0x10FFFF;
 int oflag = 0;
 char outfile[256];
 
@@ -569,7 +569,7 @@ struct font* bdf_read_font(char *path)
 int bdf_read_header(FILE *fp, struct font* pf)
 {
     int encoding;
-    int firstchar = 65535;
+    int firstchar = 0x10FFFF;
     int lastchar = -1;
     char buf[256];
     char facename[256];

tools/convttf.c

@@ -91,7 +91,7 @@ static int eid = DEFAULT_ENCODING_ID;
 static FT_UShort nocmap;
 
 int pct                     = 0; /* display ttc table if it is not zero. */
-FT_Long         max_char    = 65535;
+FT_Long         max_char    = 0x10FFFF;
 int             pixel_size  = 15;
 FT_Long         start_char  = 0;
 FT_Long         limit_char;