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Hash : e83d08dd
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Date : 2024-02-23T17:10:15

keysyms: Fast and complete case mappings (Unicode 15.1)

The current code to handle keysym case mappings is quite complex and
slow. It is also incomplete, as it does not cover recent Unicode
database. Finally, it does not handle title case correctly.

It would be easier if we were to use only a lookup table, but a trivial
implementation would lead to a huge array: the cased characters range
from `U+0041` to `U+`1F189, i.e. a span of 127 304 elements.

Thus we need some tricks to compress the lookup table. We based our
work on the post:
https://github.com/apankrat/notes/blob/3c551cb028595fd34046c5761fd12d1692576003/fast-case-conversion/README.md

The compression algorithm is roughly:
1. Compute the delta between the characters and their mappings.
2. Split the delta array in chunk of a given size.
3. Rearrange the order of the chunks in order to optimize consecutive
   chunks overlap.
4. Create a data table with the reordered chunks and an index table
   that maps the original chunk index to its offset in the data table.

The compression algorithm is then applied a second time to the previous
index table.

The complete algorithm optimizes the two chunk sizes in order to get
the lowest total data size.

The mappings were generated using CPython 3.12.4, PyICU 2.13, PyYaml
6.0.1 and ICU 75.1.

Also:
- Added explicit list of named keysyms and their case mappings.
- Added benchmark for case mappings.
- Rework ICU tests.

Note: 13b30f4f0dccc08dfea426d73570b913596ed602 introduced a fix for
sharp S `U+00DF`. With the new implementation, the *conversion*
functions `xkb_keysym_to_{lower,upper}` leave it *unchanged*, while
the *predicate* functions `xkb_keysym_is_{lower,upper_or_title}`
produce the expected results:

```c
xkb_keysym_to_upper(XKB_KEY_ssharp) == XKB_KEY_ssharp;
xkb_keysym_to_lower(XKB_KEY_ssharp) == XKB_KEY_ssharp;
xkb_keysym_to_lower(XKB_KEY_Ssharp) == XKB_KEY_ssharp;

xkb_keysym_is_lower         (XKB_KEY_ssharp) == true;
xkb_keysym_is_upper_or_title(XKB_KEY_Ssharp) == true;
```

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