[build] add printf literal string format checks for va_list functions (#12236)

This commit introduces enhanced format string checking. It activates a
new compiler warning to identify potential issues with non-literal
format strings and systematically applies format attribute macros to
functions that handle variable arguments.

etc/gn/toolchain/BUILD.gn

@@ -31,6 +31,7 @@ toolchain("toolchain") {
     "-Wall",
     "-Wextra",
     "-Wundef",
+    "-Wformat-nonliteral",
   ]
   if (use_clang) {
     cc = "clang"