This treats compiled functions homogeneously, removing the need to add new
metadata tables to places like `CompiledModuleInfo` whenever we add a new kind
of function, and simplifying the process of constructing the metadata for a
final, linked compilation artifact. This also paves the way to doing gc-sections
in our linking (getting smaller code sizes, removing functions that have been
inlined into every caller, and etc...) as we no longer assume that certain types
of function index spaces are dense.

This does, however, replace a couple operations that were previously O(1) table
lookups with O(log n) binary searches. And, notably, some of these are on the
`VMFuncRef`-creation path, and therefore on the
force-initialization-of-a-lazy-funcref-table-slot path, when we look up a Wasm
function and its trampolines. Our call-indirect micro-benchmarks show that
indirect calling every funcref once in a table of 64Ki slots went from taking
~2.6ms to ~3.8ms (a +46% slowdown). Note that this edge case is both synthetic
and the worst-case scenario for this commit's change: we are measuring, as much
as we can, *only* the force-initialization-of-a-lazy-funcref-table-slot
path. All other call-indirect benchmarks are within the noise, which is what we
would expect.

Also, the size of `.cwasm`s is slightly larger: `spidermonkey.wasm`'s `.cwasm`
size went from `19_750_632` bytes to `19785872` bytes, which is a 1.78%
increase.

Ultimately, I believe that the simplification and possibility of doing
gc-sections in the future is worth the downsides. That said, if others feel
differently, there are some things we could try to improve the situation,
although most things I can think of off the top of my head (e.g. LEB128s and
delta encoding, making certain `FuncKey` kinds' index spaces dense) will improve
one of code size or lookup times while pessimizing the other. I'm sure we could
come up with something given enough effort though.

<details>

<summary>call-indirect micro-benchmarks results</summary>

```
call-indirect/same-callee/table-init-lazy/65536-calls
                        time:   [144.14 µs 145.26 µs 146.56 µs]
                        thrpt:  [447.15 Melem/s 451.15 Melem/s 454.68 Melem/s]
                 change:
                        time:   [−5.5066% −3.6611% −1.9130%] (p = 0.00 < 0.05)
                        thrpt:  [+1.9503% +3.8002% +5.8275%]
                        Performance has improved.
Found 9 outliers among 100 measurements (9.00%)
  7 (7.00%) high mild
  2 (2.00%) high severe
call-indirect/different-callees/table-init-lazy/65536-calls
                        time:   [3.8128 ms 3.8433 ms 3.8763 ms]
                        thrpt:  [16.907 Melem/s 17.052 Melem/s 17.188 Melem/s]
                 change:
                        time:   [+43.064% +46.066% +49.080%] (p = 0.00 < 0.05)
                        thrpt:  [−32.922% −31.538% −30.101%]
                        Performance has regressed.
Found 7 outliers among 100 measurements (7.00%)
  7 (7.00%) high mild
call-indirect/same-callee/table-init-strict/65536-calls
                        time:   [130.27 µs 131.66 µs 133.40 µs]
                        thrpt:  [491.26 Melem/s 497.75 Melem/s 503.09 Melem/s]
                 change:
                        time:   [−6.4798% −4.1871% −1.8965%] (p = 0.00 < 0.05)
                        thrpt:  [+1.9332% +4.3701% +6.9288%]
                        Performance has improved.
Found 12 outliers among 100 measurements (12.00%)
  4 (4.00%) high mild
  8 (8.00%) high severe
call-indirect/different-callees/table-init-strict/65536-calls
                        time:   [176.22 µs 178.49 µs 180.99 µs]
                        thrpt:  [362.10 Melem/s 367.18 Melem/s 371.90 Melem/s]
                 change:
                        time:   [−18.431% −15.397% −12.330%] (p = 0.00 < 0.05)
                        thrpt:  [+14.064% +18.200% +22.595%]
                        Performance has improved.
Found 7 outliers among 100 measurements (7.00%)
  4 (4.00%) high mild
  3 (3.00%) high severe
```

</details>

It is required at runtime not just compile time now.