es-MX FixedDecimalFormatter data seems to be missing

[sven-oly]

es-MX uses . for the decimal separator:

https://github.com/unicode-org/cldr-json/blob/main/cldr-json/cldr-numbers-full/main/es-MX/numbers.json

However, the ICU4X data file has no entry for es-MX or for es-419, meaning that es-MX falls back to es data, which uses , as the decimal separator:

https://github.com/unicode-org/icu4x/blob/main/provider/baked/decimal/data/macros/decimal_symbols_v1.rs.data

[sffc]

Verbose datagen output:

2023-10-27T02:01:00.599Z TRACE [icu_datagen::driver] Generating key/locale: decimal/symbols@1/es-MX
2023-10-27T02:01:00.839Z TRACE [icu_datagen::driver] Deduplicating decimal/symbols@1/es-MX (inherits from es-419)
2023-10-27T02:01:00.826Z TRACE [icu_datagen::driver] Deduplicating decimal/symbols@1/es-419 (inherits from und)

But es-419 does not inherit from und.

[sffc]

The problem was that the runtime fallback mode was deduplicating locales that had any parent with equal data, but it should have been deduplicating locales only if the closest parent had equal data. This affected es-MX because it has the same data as und, but it has different data than es, which was being reached by fallback. (There were other locales besides es-MX which were impacted.)

This affected data in the following components:

• icu_compactdecimal
• icu_datetime
• icu_decimal
• icu_displaynames
• icu_properties