Get rid of high-level FFI suffixed options structs in 2.0

[Manishearth]

Related: #3790

Part of #2856

Currently over FFI we do things like ICU4XCollatorOptionsV1 (and functions accepting it are named like create_v1() so that the options structs can be evolved in the future.

At a high level, once rust-diplomat/diplomat#247 and rust-diplomat/diplomat#271 are fixed, we should keep the Rust struct names (as they map to C struct/function names), but we can diplomat-rename ICU4XCollatorOptionsV1 to icu4x::CollatorOptions, and create_v1() to create().

When in the future we add more fields, we create a ICU4XCollatorOptionsV2 and create_v2, hook it up with defaults infrastructure so that old code constructing the old options bags will seamlessly work, and then move the diplomat-renames over to these new APIs whilst diplomat-disabling the old ones.

This maintains ABI stability (the old methods are available and unchanged), and is seamless from the perspective of higher-level API users.

I would like this to be solved for 2.0.

[Manishearth]

@sffc we never ended up investigating rust-diplomat/diplomat#271, and at this point I don't think we can do much here, we'll have to keep these as suffixed. Unsuffixing them in C++ will require getting rid of braced initialization entirely, and I don't think we should do that.

I'm removing this from the milestone, but we may wish to revisit this in the future.