Updated DEC Line Graphics character set to use Unicode 3.2.0 characters where appropriate

Four characters in DEC Special Graphics (Line Drawing)[⁽¹⁾] charset were translated by Konsole into codepoints in private use area.

This patch uses the same code points that xterm uses.

| Index  | Previously | Should be |
| ------ | ---------- | ----------|
| `0x6F` | `U+F800`   | `U+23BA`  |
| `0x70` | `U+F801`   | `U+23BB`  |
| `0x72` | `U+F803`   | `U+23BC`  |
| `0x73` | `U+F804`   | `U+23BD`  |

The old behavior used the same mapping used by Linux consoles, as stated
in `unicode.txt`[⁽²⁾] in Linux's documents. This has been changed long ago
when Unicode 3.2.0 introduced the codepoints `U+23BA`, `U+23BB`, `U+23BC`,
`U+23BD`, as the following excerpt of `unicode.txt` says:

```
In addition, the following characters not present in Unicode 1.1.4
have been defined; these are used by the DEC VT graphics map.  [v1.2]
THIS USE IS OBSOLETE AND SHOULD NO LONGER BE USED; PLEASE SEE BELOW.

====== ======================================
U+F800 DEC VT GRAPHICS HORIZONTAL LINE SCAN 1
U+F801 DEC VT GRAPHICS HORIZONTAL LINE SCAN 3
U+F803 DEC VT GRAPHICS HORIZONTAL LINE SCAN 7
U+F804 DEC VT GRAPHICS HORIZONTAL LINE SCAN 9
====== ======================================

[...]

[v1.3]: These characters have been officially added to Unicode 3.2.0;
they are added at U+23BA, U+23BB, U+23BC, U+23BD.  Linux now uses the
new values.
```

[⁽¹⁾]: https://vt100.net/docs/vt220-rm/chapter2.html#T2-4
[⁽²⁾]: https://raw.githubusercontent.com/torvalds/linux/5bfc75d92efd494db37f5c4c173d3639d4772966/Documentation/admin-guide/unicode.rst