perf: skip LOGF formatting when logging is silent

LOGF/LOGF_COLOR always ran fmt::sprintf even when the output was discarded; at
emulator log volume the formatting alone costs frames. Add Log::IsSilent() and
short-circuit before formatting. Behavior-preserving on all platforms (it only
skips work whose result is thrown away); before init it reports non-silent so
early logs still print.

(cherry picked from commit 1749e0fc68ae4290055fb12f72c9bb4baf466190)

src/common/logging/log.cpp

@@ -178,6 +178,11 @@ Direction GetDirection() {
 	return g_direction;
 }
 
+bool IsSilent() {
+	// Before init LOGF must keep writing to stdout, so report non-silent.
+	return g_initialized && g_direction == Direction::Silent;
+}
+
 void Write(std::string_view text) {
 	WriteImpl(text);
 }