Kernel/Graphics + SystemServer: Support text mode properly

As we removed the support of VBE modesetting that was done by GRUB early
on boot, we need to determine if we can modeset the resolution with our
drivers, and if not, we should enable text mode and ensure that
SystemServer knows about it too.

Also, SystemServer should first check if there's a framebuffer device
node, which is an indication that text mode was not even if it was
requested. Then, if it doesn't find it, it should check what boot_mode
argument the user specified (in case it's self-test). This way if we
try to use bochs-display device (which is not VGA compatible) and
request a text mode, it will not honor the request and will continue
with graphical mode.

Also try to print critical messages with mininum memory allocations
possible.

In LibVT, We make the implementation flexible for kernel-specific
methods that are implemented in ConsoleImpl class.

Userland/Libraries/LibVT/Terminal.h

@@ -12,9 +12,18 @@
 #include <AK/Vector.h>
 #include <Kernel/API/KeyCode.h>
 #include <LibVT/EscapeSequenceParser.h>
-#include <LibVT/Line.h>
 #include <LibVT/Position.h>
 
+#ifndef KERNEL
+#    include <LibVT/Attribute.h>
+#    include <LibVT/Line.h>
+#else
+namespace Kernel {
+class VirtualConsole;
+}
+#    include <LibVT/Attribute.h>
+#endif
+
 namespace VT {
 
 class TerminalClient {
@@ -31,24 +40,52 @@ public:
 
 class Terminal : public EscapeSequenceExecutor {
 public:
+#ifndef KERNEL
     explicit Terminal(TerminalClient&);
-    ~Terminal();
+#else
+    explicit Terminal(Kernel::VirtualConsole&);
+#endif
+
+    virtual ~Terminal()
+    {
+    }
 
     bool m_need_full_flush { false };
 
+#ifndef KERNEL
     void invalidate_cursor();
+#else
+    virtual void invalidate_cursor() = 0;
+#endif
+
     void on_input(u8);
 
+    void set_cursor(unsigned row, unsigned column);
+
+#ifndef KERNEL
     void clear();
     void clear_including_history();
+#else
+    virtual void clear() = 0;
+    virtual void clear_including_history() = 0;
+#endif
 
+#ifndef KERNEL
     void set_size(u16 columns, u16 rows);
-    u16 columns() const { return m_columns; }
+#else
+    virtual void set_size(u16 columns, u16 rows) = 0;
+#endif
+
+    u16 columns() const
+    {
+        return m_columns;
+    }
     u16 rows() const { return m_rows; }
 
     u16 cursor_column() const { return m_cursor_column; }
     u16 cursor_row() const { return m_cursor_row; }
 
+#ifndef KERNEL
     size_t line_count() const
     {
         return m_history.size() + m_lines.size();
@@ -100,13 +137,16 @@ public:
         m_max_history_lines = value;
     }
     size_t history_size() const { return m_history.size(); }
+#endif
 
     void inject_string(const StringView&);
     void handle_key_press(KeyCode, u32, u8 flags);
 
+#ifndef KERNEL
     Attribute attribute_at(const Position&) const;
+#endif
 
-private:
+protected:
     // ^EscapeSequenceExecutor
     virtual void emit_code_point(u32) override;
     virtual void execute_control_code(u8) override;
@@ -117,14 +157,20 @@ private:
     virtual void receive_dcs_char(u8 byte) override;
     virtual void execute_dcs_sequence() override;
 
+    void carriage_return();
+#ifndef KERNEL
     void scroll_up();
     void scroll_down();
     void newline();
-    void carriage_return();
-
-    void set_cursor(unsigned row, unsigned column);
     void put_character_at(unsigned row, unsigned column, u32 ch);
     void set_window_title(const String&);
+#else
+    virtual void scroll_up() = 0;
+    virtual void scroll_down() = 0;
+    virtual void newline() = 0;
+    virtual void put_character_at(unsigned row, unsigned column, u32 ch) = 0;
+    virtual void set_window_title(const String&) = 0;
+#endif
 
     void unimplemented_control_code(u8);
     void unimplemented_escape_sequence(Intermediates, u8 last_byte);
@@ -192,8 +238,12 @@ private:
     // DSR - Device Status Reports
     void DSR(Parameters);
 
+#ifndef KERNEL
     // ICH - Insert Character
     void ICH(Parameters);
+#else
+    virtual void ICH(Parameters) = 0;
+#endif
 
     // SU - Scroll Up (called "Pan Down" in VT510)
     void SU(Parameters);
@@ -201,14 +251,18 @@ private:
     // SD - Scroll Down (called "Pan Up" in VT510)
     void SD(Parameters);
 
+#ifndef KERNEL
     // IL - Insert Line
     void IL(Parameters);
-
     // DCH - Delete Character
     void DCH(Parameters);
-
     // DL - Delete Line
     void DL(Parameters);
+#else
+    virtual void IL(Parameters) = 0;
+    virtual void DCH(Parameters) = 0;
+    virtual void DL(Parameters) = 0;
+#endif
 
     // CHA - Cursor Horizontal Absolute
     void CHA(Parameters);
@@ -225,10 +279,14 @@ private:
     // FIXME: Find the right names for these.
     void XTERM_WM(Parameters);
 
+#ifndef KERNEL
     TerminalClient& m_client;
+#else
+    Kernel::VirtualConsole& m_client;
+#endif
 
     EscapeSequenceParser m_parser;
-
+#ifndef KERNEL
     size_t m_history_start = 0;
     NonnullOwnPtrVector<Line> m_history;
     void add_line_to_history(NonnullOwnPtr<Line>&& line)
@@ -246,6 +304,7 @@ private:
     }
 
     NonnullOwnPtrVector<Line> m_lines;
+#endif
 
     size_t m_scroll_region_top { 0 };
     size_t m_scroll_region_bottom { 0 };
@@ -263,7 +322,9 @@ private:
     Attribute m_current_attribute;
     Attribute m_saved_attribute;
 
+#ifndef KERNEL
     u32 m_next_href_id { 0 };
+#endif
 
     Vector<bool> m_horizontal_tabs;
     u32 m_last_code_point { 0 };