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THIS USE IS OBSOLETE AND SHOULD NO LONGER BE USED; PLEASE SEE BELOW.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

doc/user/README.fonts

@@ -58,7 +58,11 @@ Fonts need to suit the needs of X11, QT and konsole.
   - 0x0d U+250c : BOX DRAWINGS LIGHT DOWN AND RIGHT
   - 0x0e U+2514 : BOX DRAWINGS LIGHT UP AND RIGHT
   - 0x0f U+253c : BOX DRAWINGS LIGHT VERTICAL AND HORIZONTAL
+  - 0x10 U+23ba : HORIZONTAL SCAN LINE-1
+  - 0x11 U+23bb : HORIZONTAL SCAN LINE-3
   - 0x12 U+2500 : BOX DRAWINGS LIGHT HORIZONTAL (scan line 5)
+  - 0x13 U+23bc : HORIZONTAL SCAN LINE-7
+  - 0x14 U+23bd : HORIZONTAL SCAN LINE-9
   - 0x15 U+251c : BOX DRAWINGS LIGHT VERTICAL AND RIGHT
   - 0x16 U+2524 : BOX DRAWINGS LIGHT VERTICAL AND LEFT
   - 0x17 U+2534 : BOX DRAWINGS LIGHT UP AND HORIZONTAL
@@ -69,17 +73,6 @@ Fonts need to suit the needs of X11, QT and konsole.
   - 0x02 U+2592 : MEDIUM SHADE
   - 0x1F U+00b7 : MIDDLE DOT
 
-  The following graphical glyphs are defined in
-  VT100 fonts, too, but are not used in any program
-  i know about. Codes for them have been assigned
-  in the private unicode page. See the linux kernel
-  documentation file [unicode.txt] about this assignment.
-
-  - 0x10 U+f800 : DEC VT GRAPHICS HORIZONTAL LINE SCAN 1
-  - 0x11 U+f801 : DEC VT GRAPHICS HORIZONTAL LINE SCAN 3
-  - 0x13 U+f803 : DEC VT GRAPHICS HORIZONTAL LINE SCAN 7
-  - 0x14 U+f804 : DEC VT GRAPHICS HORIZONTAL LINE SCAN 9
-
   Also, the VT100 knows about the following glyphs,
   though omitting them is unlikely to break anything.
 

src/Vt102Emulation.cpp

@@ -52,7 +52,7 @@ unsigned short Konsole::vt100_graphics[32] = {
     // 0/8     1/9    2/10    3/11    4/12    5/13    6/14    7/15
     0x0020, 0x25C6, 0x2592, 0x2409, 0x240c, 0x240d, 0x240a, 0x00b0,
     0x00b1, 0x2424, 0x240b, 0x2518, 0x2510, 0x250c, 0x2514, 0x253c,
-    0xF800, 0xF801, 0x2500, 0xF803, 0xF804, 0x251c, 0x2524, 0x2534,
+    0x23ba, 0x23bb, 0x2500, 0x23bc, 0x23bd, 0x251c, 0x2524, 0x2534,
     0x252c, 0x2502, 0x2264, 0x2265, 0x03C0, 0x2260, 0x00A3, 0x00b7
 };
 /* clang-format on */