[Power BI] AdvisorReservationRecommendations has two columns that differ only by case (region / Region) #2347

Problem

The AdvisorReservationRecommendations table has carried one region column for a long time: properties.extendedProperties.region up to v0.10, and properties.extendedProperties.Region from v0.11 through v14. Since #1849 (v15 milestone, not released yet), both the storage and KQL Shared.Dataset define both columns side by side:

• properties.extendedProperties.Region (AdvisorReservationRecommendations.tmdl L383)
• properties.extendedProperties.region (AdvisorReservationRecommendations.tmdl L107)

The ARG query projects both (L472 and L476), and cultures/en-US.tmdl has linguistic entries for both. Column names in a Power BI semantic model are case-insensitive, so these two names are expected to collide.

Observed

While testing #2333, the project failed to load in Power BI Desktop. I haven't confirmed that this collision caused it; the failure may have had another cause. Opening the current dev project in Desktop should confirm or rule it out.

Suggested fix

Advisor likely returns region for some recommendation types and Region for others. If so, keep one column and merge both sources in the query, for example:

['properties.extendedProperties.Region'] = coalesce(properties.extendedProperties.Region, properties.extendedProperties.region)

Then remove the lowercase column and its culture entries in both datasets. If the two fields mean different things, rename one instead.