Kernel: Avoid unnecessary allocations for TTY::tty_name()

Kernel/TTY/SlavePTY.cpp

@@ -31,7 +31,7 @@ SlavePTY::~SlavePTY()
     DevPtsFS::unregister_slave_pty(*this);
 }
 
-String SlavePTY::tty_name() const
+String const& SlavePTY::tty_name() const
 {
     return m_tty_name;
 }

Kernel/TTY/SlavePTY.h

@@ -26,7 +26,7 @@ public:
 
 private:
     // ^TTY
-    virtual String tty_name() const override;
+    virtual String const& tty_name() const override;
     virtual ssize_t on_tty_write(const UserOrKernelBuffer&, ssize_t) override;
     virtual void echo(u8) override;
 

Kernel/TTY/TTY.h

@@ -26,7 +26,7 @@ public:
     virtual int ioctl(FileDescription&, unsigned request, FlatPtr arg) override final;
     virtual String absolute_path(const FileDescription&) const override { return tty_name(); }
 
-    virtual String tty_name() const = 0;
+    virtual String const& tty_name() const = 0;
 
     unsigned short rows() const { return m_rows; }
     unsigned short columns() const { return m_columns; }

Kernel/TTY/VirtualConsole.h

@@ -35,7 +35,7 @@ private:
 
     // ^TTY
     virtual ssize_t on_tty_write(const UserOrKernelBuffer&, ssize_t) override;
-    virtual String tty_name() const override { return m_tty_name; }
+    virtual String const& tty_name() const override { return m_tty_name; }
     virtual void echo(u8) override;
 
     // ^TerminalClient