Kernel+LibC: Tidy up sys$ttyname() and sys$ptsname()

- Remove goofy _r suffix from syscall names.
- Don't take a signed buffer size.
- Use Userspace<T>.
- Make TTY::tty_name() return a String instead of a StringView.

Kernel/TTY/SlavePTY.cpp

@@ -54,7 +54,7 @@ SlavePTY::~SlavePTY()
     DevPtsFS::unregister_slave_pty(*this);
 }
 
-StringView SlavePTY::tty_name() const
+String SlavePTY::tty_name() const
 {
     return m_tty_name;
 }

Kernel/TTY/SlavePTY.h

@@ -42,7 +42,7 @@ public:
 
 private:
     // ^TTY
-    virtual StringView tty_name() const override;
+    virtual String tty_name() const override;
     virtual ssize_t on_tty_write(const u8*, ssize_t) override;
     virtual void echo(u8) override;
 

Kernel/TTY/TTY.h

@@ -46,7 +46,7 @@ public:
     virtual int ioctl(FileDescription&, unsigned request, FlatPtr arg) override final;
     virtual String absolute_path(const FileDescription&) const override { return tty_name(); }
 
-    virtual StringView tty_name() const = 0;
+    virtual String tty_name() const = 0;
 
     unsigned short rows() const { return m_rows; }
     unsigned short columns() const { return m_columns; }

Kernel/TTY/VirtualConsole.h

@@ -55,7 +55,7 @@ private:
 
     // ^TTY
     virtual ssize_t on_tty_write(const u8*, ssize_t) override;
-    virtual StringView tty_name() const override { return m_tty_name; }
+    virtual String tty_name() const override { return m_tty_name; }
     virtual void echo(u8) override;
 
     // ^TerminalClient