bug#57072: [BUG] update-glyphless-char-display and variation selectors

[Axel Svensson <svenssonaxel@gmail.com>]

> What does Unicode say about the functionality of the variation
> selectors beyond VS-16?

The code charts divide them into three groups:
- VS1 through VS14 are "Variation selectors" [1]
- VS15 through VS16 are "Emoji-specific variation selectors" [1]
- VS17 through VS256 are "Ideographic-specific variation selectors" [2]

The standard itself in chapter 23.4 [3] makes no distinction between
them but say that the only sanctioned uses that should have any effect,
are the ones defined in:
- StandardizedVariants.txt [4] in the Unicode Character Database, which
  currently uses only VS1 through VS3. Confusingly though, some of them
  seem to be used for ideographic purposes.
- Unicode Technical Standard #51 for emojis [5], which says that VS15 is
  "used to request a text presentation for an emoji character" while
  VS16 is "used to request an emoji presentation for an emoji
  character".
- Unicode Technical Standard #37 for ideographic variation [6], which
  confirms that it only uses VS17 through VS256.

In any case, it seems that admin/unidata/blocks.awk needs fixing, since
it currently handles only VS1 through VS16 and does so as if they were
all for emoji use.

[1] https://www.unicode.org/charts/PDF/UFE00.pdf
[2] https://www.unicode.org/charts/PDF/UE0100.pdf
[3] https://www.unicode.org/versions/Unicode14.0.0/ch23.pdf
[4] https://www.unicode.org/Public/14.0.0/ucd/StandardizedVariants.txt
[5] https://www.unicode.org/reports/tr51/#Emoji_Variation_Sequences
[6] https://www.unicode.org/reports/tr37/