Fix: Add missing cstdint header

[FredeHoey]

I ran into this trying to compile the project using GCC. It complained about uint8_t being undefined. This fixes that.

[martinetd]

Thank you, I've confirmed build broke with gcc15

There are some deprecated warnings left (around wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> being deprecated), but this at least makes the build pass for all targets, so this looks good to me.

This repo is being moved away from, I've re-opened the PR on flutter-elinux#2 after adjusting the commit message -- I'll merge it over there if you're ok with the new commit message (as you're still author)

[martinetd]

Ah, should also add your name to the AUTHORS file if you'd like -- since you can't update that PR, please let me know and I'll add you (as per git commit message author name/email)

(Given we have git log I'm not convinced on the usefulness of the file, but it's not my place to change that at this point)