Add icu_properties feature to icu_normalizer

[Manishearth]

Fixes #5121

[sffc]

error[E0599]: no method named `get32` found for struct `CanonicalCombiningClassMapBorrowed` in the current scope
  --> ffi/capi/src/normalizer_properties.rs:54:34
   |
54 |             self.0.as_borrowed().get32(ch).0
   |                                  ^^^^^ help: there is a method with a similar name: `get32_u8`

For more information about this error, try `rustc --explain E0599`.
error: could not compile `icu_capi` (lib) due to previous error

[hsivonen]

Thanks. This needs testing with Pernosco to see if this breaks Pernosco's special knowledge about the ICU4X types involved here. I'll test and will report back.

[hsivonen]

I created a new crate that depends on icu_normalizer by path, and building the new crate ends up building icu_properties anyway. Is this changeset accomplishing what's intended?

[hsivonen]

This changeset with or without the feature enabled breaks Pernosco's rendering of the CharacterAndClass type.

Without this PR:
self ::CharacterAndClass*@0x7285c15ff1b8={char=‘⁨̧⁩’ 0x327, ccc=(202 ‘Ê’)}

With this PR:
self ::CharacterAndClass*@0x7eacb49ff1b8=(3388998439)

I think this should not be merged as-is.

I'm not quite sure what precisely Pernosco wants to see. I suggest putting the accessors on CharacterAndClass that have CanonicalCombiningClass in the return value behind the feature and introducing differently-named u8 accessors. (I haven't yet tested if that would work.)

[hsivonen]

I created a new crate that depends on icu_normalizer by path, and building the new crate ends up building icu_properties anyway. Is this changeset accomplishing what's intended?

I pushed a change to restore Pernosco compat. (That took way more rounds of experimentation than I expected!) However, the above observation still applies: icu_properties gets compiled when the icu_properties feature isn't set. Why?

[robertbastian]

nit: define type CanonicalCombiningClass = u8 or a newtype, and then qualify the properties one?

[Manishearth]

This is a good idea, I did one better, I wrote a seamless shim type CanonicalCombiningClass(pub u8) that gets imported in non-properties mode.

[Manishearth]

However, the above observation still applies: icu_properties gets compiled when the icu_properties feature isn't set. Why?

It's because I didn't switch to ? deps. I fixed it.