Implement generalized decimal pattern parsing

[sffc]

In #541, I use a temporary decimal pattern parsing algorithm as a placeholder for the main one that we will need to write in order to handle the full spectrum of CLDR data.

This algorithm will need to:

• Handle quoted literals in prefix and suffix
• Support currency symbols, including at the decimal separator (https://github.com/unicode-org/cldr/pull/1137)
• Support grouping digits in the fraction

I think we should consider following a model similar to that in DateTimeFormat, where we have a public Pattern type, which is serializable and allowed to live in the data struct, with a human-readable representation for JSON and a machine-readable representation for Bincode (and rkyv).

[gregtatum]

I think we should consider following a model similar to that in DateTimeFormat, where we have a public Pattern type, which is serializable and allowed to live in the data struct, with a human-readable representation for JSON and a machine-readable representation for Bincode (and rkyv).

👍

[sffc]

Dependency of #275

[sffc]

@younies is going to take a look at this.

[sffc]

Needed for currency. Assigning to @robertbastian