Follow up to #8810

Same reasoning.

This commit changes a LOT of areas of the code to use decl literals
instead of redundantly referring to the type.

These changes were mostly driven by some regex searches and then manual
adjustment on a case-by-case basis.

I almost certainly missed quite a few places where decl literals could
be used, but this is a good first step in converting things, and other
instances can be addressed when they're discovered.

I tested GLFW+Metal and building the framework on macOS and tested a GTK
build on Linux, so I'm 99% sure I didn't introduce any syntax errors or
other problems with this. (fingers crossed)

Not linking libc avoids potential problems when compiling from/for certain targets (see https://github.com/ghostty-org/ghostty/discussions/3218), and using an ArenaAllocator makes unigen run just as fast (in both release and debug modes) while also taking less memory.

Benchmark 1 (3 runs): ./zig-out/bin/unigen-release-c
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          1.75s  ± 15.8ms    1.73s  … 1.76s           0 ( 0%)        0%
  peak_rss           2.23MB ±    0      2.23MB … 2.23MB          0 ( 0%)        0%
  cpu_cycles         7.22G  ± 62.8M     7.16G  … 7.29G           0 ( 0%)        0%
  instructions       11.5G  ± 16.0      11.5G  … 11.5G           0 ( 0%)        0%
  cache_references    436M  ± 6.54M      430M  …  443M           0 ( 0%)        0%
  cache_misses        310K  ±  203K      134K  …  532K           0 ( 0%)        0%
  branch_misses      1.03M  ± 29.9K      997K  … 1.06M           0 ( 0%)        0%
Benchmark 2 (3 runs): ./zig-out/bin/unigen-release-arena
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          1.73s  ± 6.40ms    1.72s  … 1.73s           0 ( 0%)          -  1.0% ±  1.6%
  peak_rss           1.27MB ± 75.7KB    1.18MB … 1.31MB          0 ( 0%)        ⚡- 43.1% ±  5.4%
  cpu_cycles         7.16G  ± 26.5M     7.13G  … 7.18G           0 ( 0%)          -  0.9% ±  1.5%
  instructions       11.4G  ± 28.2      11.4G  … 11.4G           0 ( 0%)          -  0.8% ±  0.0%
  cache_references    441M  ± 2.89M      439M  …  444M           0 ( 0%)          +  1.2% ±  2.6%
  cache_misses        152K  ±  102K     35.2K  …  220K           0 ( 0%)          - 50.8% ± 117.8%
  branch_misses      1.05M  ± 13.4K     1.04M  … 1.06M           0 ( 0%)          +  2.0% ±  5.1%

Benchmark 1 (3 runs): ./zig-out/bin/unigen-debug-c
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          1.75s  ± 32.4ms    1.71s  … 1.77s           0 ( 0%)        0%
  peak_rss           2.23MB ±    0      2.23MB … 2.23MB          0 ( 0%)        0%
  cpu_cycles         7.23G  ±  136M     7.08G  … 7.34G           0 ( 0%)        0%
  instructions       11.5G  ± 37.9      11.5G  … 11.5G           0 ( 0%)        0%
  cache_references    448M  ± 1.03M      447M  …  449M           0 ( 0%)        0%
  cache_misses        148K  ± 42.6K     99.3K  …  180K           0 ( 0%)        0%
  branch_misses       987K  ± 5.27K      983K  …  993K           0 ( 0%)        0%
Benchmark 2 (3 runs): ./zig-out/bin/unigen-debug-arena
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          1.76s  ± 4.12ms    1.76s  … 1.76s           0 ( 0%)          +  0.4% ±  3.0%
  peak_rss           1.22MB ± 75.7KB    1.18MB … 1.31MB          0 ( 0%)        ⚡- 45.1% ±  5.4%
  cpu_cycles         7.27G  ± 17.1M     7.26G  … 7.29G           0 ( 0%)          +  0.6% ±  3.0%
  instructions       11.4G  ± 3.79      11.4G  … 11.4G           0 ( 0%)          -  0.8% ±  0.0%
  cache_references    440M  ± 4.52M      435M  …  444M           0 ( 0%)          -  1.7% ±  1.7%
  cache_misses       43.6K  ± 19.2K     26.5K  … 64.3K           0 ( 0%)        ⚡- 70.5% ± 50.8%
  branch_misses      1.04M  ± 2.25K     1.04M  … 1.05M           0 ( 0%)        💩+  5.8% ±  0.9%

Fixes #2941

This fixes the rendering of the text below. For those that can't see it,
it is the following in UTF-32: `0x22 0x1F3FF 0x22`.

```
"🏿"
```

`0x1F3FF` is the Fitzpatrick modifier for dark skin tone. It has the
Unicode property `Emoji_Modifier`. Emoji modifiers are defined in UTS
#51 and are only valid based on ED-13:

```
emoji_modifier_sequence := emoji_modifier_base emoji_modifier
emoji_modifier_base := \p{Emoji_Modifier_Base}
emoji_modifier := \p{Emoji_Modifier}
```

Additional quote from UTS #51:

> To have an effect on an emoji, an emoji modifier must immediately follow
> that base emoji character. Emoji presentation selectors are neither needed
> nor recommended for emoji characters when they are followed by emoji
> modifiers, and should not be used in newly generated emoji modifier
> sequences; the emoji modifier automatically implies the emoji presentation
> style.

Our precomputed grapheme break table was mistakingly not following this
rule. This commit fixes that by adding a check for that every
`Emoji_Modifier` character must be preceded by an `Emoji_Modifier_Base`.
This only has a cost during compilation (table generation). The runtime
cost is identical; the table size didn't increase since we had leftover
bits we could use.