feat: implement core initialization and local APIC setup

kernel/include/apic/lapic.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "acpi/discovery.h"
+#include "util/number.h"
+
+namespace apic {
+
+using lapic_id_t = uint32_t;
+
+void initLocalApic(const acpi::discovery_result_t& discovery);
+
+lapic_id_t localApicId();
+
+void sendInit(lapic_id_t destination);
+
+// startup_page: physical address of the real-mode entry point divided by 4096;
+// must point below 1 MiB, so only values < 0x100 are meaningful.
+void sendStartup(lapic_id_t destination, uint8_t startup_page);
+
+void sendInterrupt(lapic_id_t destination, uint8_t vector);
+
+void signalEndOfInterrupt();
+
+} // namespace apic