Replace std::snprintf() with wpi::format_to_n_c_str() (#5645)

fmtlib uses consteval format string processing, which makes it more
efficient than std::snprintf().

snprintf()s in libuv, mpack, processstarter, and wpigui were left alone.
processstarter uses stdlib only, and wpigui only depends on imgui.

fmt::format_to_n() is analogous to std::format_to_n()
(https://en.cppreference.com/w/cpp/utility/format/format_to_n)

wpi::format_to_n_c_str() is a wrapper which adds the trailing NUL.

glass/src/lib/native/cpp/Context.cpp

@@ -6,7 +6,6 @@
 
 #include <algorithm>
 #include <cinttypes>
-#include <cstdio>
 #include <filesystem>
 
 #include <fmt/format.h>
@@ -533,7 +532,8 @@ void glass::PushID(const char* str_id_begin, const char* str_id_end) {
 
 void glass::PushID(int int_id) {
   char buf[16];
-  std::snprintf(buf, sizeof(buf), "%d", int_id);
+  wpi::format_to_n_c_str(buf, sizeof(buf), "{}", int_id);
+
   PushStorageStack(buf);
   ImGui::PushID(int_id);
 }