Improve built-in line/block characters drawing

Summary:
* Fix bold lines (BUG 402415).
* Make drawing pixel-perfect.
* Make line width proportional to font size.
* Move relevant code to separate file and namespace.
* Remove code for checking supported line characters from Character
  class. Information about what is supported is now in one place
  together width drawing code.
* Remove fontembedder/LineFont files (no longer used).
* Add test script for displaying supported characters table.
* Add triple and quadruple dashes (U+2504...U+250B).
* Change shade block characters (U+2591...U+2593) look. When
  antialiasing is turned on, shades are drawn as transculent solid
  rectangles with 25%, 50% and 75% alpha. This matches the characters
  name/description and their usage. Without antialiasing, previous
  method with patterns is used.

**Screenshots**

Font size: 10pt; character width: 8px
{F6602823}

Font size: 11pt; character width: 9px
{F6602824}

Font size: 12pt; character width: 10px
{F6602825}

Font size: 13-14pt; character width: 11px; w/o antialiasing
{F6602826}

Font size: 13-14pt; character width: 11px
{F6602827}

Font size: 15pt; character width: 12px
{F6602828}

Font size: 6-7pt; character width: 5px
{F6602829}

Font size: 8-9pt; character width: 7px; w/o antialiasing
{F6602830}

Font size: 8-9pt; character width: 7px
{F6602831}

Alignment test (8pt)
{F6602832}

Note: Copyrights in LineBlockCharactersDrawer.cpp are based on
`git blame -w src/TerminalDisplay.cpp` executed before moving the code
to a separate file. Years from first/last commit. Authors sorted by
year. Whitespace-only changes were ignored. Maksim's code was commited
by Waldo Bastian who mentioned him as the author in commit message
(see 5062b40d).

BUG: 402415

Test Plan:
== Common steps for all tests ==

* Open //Edit Current Profile → Appearance//.
* Turn on //Draw intense colors in bold font//.
* Turn off //Use line characters contained in font//.
* (Optional) select a font which is able to display bold characters in
  Konsole (e.g. DejaVu Sans Mono).

== Check characters validity ==

* Run `./tests/line_block_characters_table.py`.
* Open //Edit Current Profile → Appearance//.
* By switching //Use line characters contained in font// on and off,
  compare built-in characters drawing with characters from a font.
  General shape and line directions must be the same. Small offsets,
  line width differences (as long as proportions between lines in
  a character are kept), and quality differences are allowed.

== Review overall quality ==

* Run `./tests/line_block_characters_table.py`.
* Review glyphs quality in different font sizes.
* Open //Edit Current Profile → Appearance//.
* Toggle //Smooth fonts//, review quality again.

== Check alignment ==

* Display `tests/UTF-8-demo.txt`
* At the bottom of the file you can find a few alignment images. Check
  if all lines align properly. If you're unsure how it should look,
  compare it with font characters by turning on //Use line characters
  contained in font// option.

Reviewers: #konsole, #vdg, fvogt, hindenburg

Reviewed By: #konsole, hindenburg

Subscribers: hindenburg, sandsmark, fvogt, konsole-devel

Tags: #konsole

Differential Revision: https://phabricator.kde.org/D18735