Add stdint.h to utf8 extension

[bobf]

I don't know C++ but this made your plugin work for me, feel free to adjust/ignore if I'm doing something wrong, but either way thank you for the plugin, it seems to be working great. 🙏

Fixes failure:

[ 94%] Building CXX object CMakeFiles/textmate.dir/libs/tm-parser/textmate/extensions/utf8.cpp.o
In file included from /home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:1:
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.h:8:23: error: ‘uint32_t’ was not declared in this scope
    8 | int codepoint_to_utf8(uint32_t utf, char* out);
      |                       ^~~~~~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.h:5:1: note: ‘uint32_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
    4 | #include <string>
  +++ |+#include <cstdint>
    5 | // #include <stdint.h>
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.h:8:37: error: expected primary-expression before ‘char’
    8 | int codepoint_to_utf8(uint32_t utf, char* out);
      |                                     ^~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.h:8:46: error: expression list treated as compound expression in initializer [-fpermissive]
    8 | int codepoint_to_utf8(uint32_t utf, char* out);
      |                                              ^
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:34:5: error: redefinition of ‘int codepoint_to_utf8’
   34 | int codepoint_to_utf8(uint32_t utf, char* out)
      |     ^~~~~~~~~~~~~~~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.h:8:5: note: ‘int codepoint_to_utf8’ previously defined here
    8 | int codepoint_to_utf8(uint32_t utf, char* out);
      |     ^~~~~~~~~~~~~~~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:34:23: error: ‘uint32_t’ was not declared in this scope
   34 | int codepoint_to_utf8(uint32_t utf, char* out)
      |                       ^~~~~~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:2:1: note: ‘uint32_t’ is defined in header ‘<cstdint>’; did you forget to ‘#include <cstdint>’?
    1 | #include "utf8.h"
  +++ |+#include <cstdint>
    2 |
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:34:37: error: expected primary-expression before ‘char’
   34 | int codepoint_to_utf8(uint32_t utf, char* out)
      |                                     ^~~~
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp: In function ‘std::string wstring_to_utf8string(std::wstring)’:
/home/bob/dev/nvim-textmate/libs/tm-parser/textmate/extensions/utf8.cpp:77:26: error: ‘codepoint_to_utf8’ cannot be used as a function
   77 |         codepoint_to_utf8(c, (char*)tmp);
      |         ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
make[3]: *** [CMakeFiles/textmate.dir/build.make:272: CMakeFiles/textmate.dir/libs/tm-parser/textmate/extensions/utf8.cpp.o] Error 1
make[2]: *** [CMakeFiles/Makefile2:111: CMakeFiles/textmate.dir/all] Error 2
make[1]: *** [Makefile:91: all] Error 2
make[1]: Leaving directory '/home/bob/dev/nvim-textmate/build'
make: *** [Makefile:11: build] Error 2