[boot] Add framebuffer progress bar

After exiting UEFI, the bootloader had no way of displaying status to
the user. Now it will display a series of small boxes as a progress bar
along the bottom of the screen if a framebuffer exists. Errors or
warnings during a step will cause that step's box to turn red or orange,
and display bars above it to signal the error code.

This caused the simplification of the error handling system (which was
mostly just calling status_line::fail) and added different types of
status objects.

src/boot/error.h

@@ -14,48 +14,7 @@ namespace error {
 /// Halt or exit the program with the given error status/message
 [[ noreturn ]] void raise(uefi::status status, const wchar_t *message);
 
-/// Interface for error-handling functors
-class handler
-{
-public:
-	/// Constructor must be called by implementing classes.
-	handler();
-	virtual ~handler();
-
-	/// Interface for implementations of error handling.
-	virtual void handle(uefi::status, const wchar_t*) = 0;
-
-private:
-	friend void raise(uefi::status, const wchar_t *);
-
-	handler *m_next;
-	static handler *s_current;
-};
-
-/// Error handler using UEFI boot services. Integrates with `status_line`
-/// to print formatted error messages to the screen.
-class uefi_handler :
-	public handler
-{
-public:
-	uefi_handler(console &con);
-	virtual ~uefi_handler() {}
-	void handle(uefi::status, const wchar_t*) override;
-
-private:
-	console &m_con;
-};
-
-/// Error handler that doesn't rely on UEFI. Sets status into CPU
-/// registers and then causes a CPU #DE exception.
-class cpu_assert_handler :
-	public handler
-{
-public:
-	cpu_assert_handler();
-	virtual ~cpu_assert_handler() {}
-	void handle(uefi::status, const wchar_t*) override;
-};
+const wchar_t * message(uefi::status status);
 
 } // namespace error
 } // namespace boot