Search: Improve swagger documentation

[heaths]

Since we generate most of the code, there are a lot of descriptions in swagger that need to be improved. They either aren't clear (e.g. almost all enum value description), or just wrong (e.g. PatternAnalyzer.Pattern description says it defaults to whitespace when, actually, it's non-whitespace, i.e. \w+).

This will positively improve all languages' SDKs and means we don't have to override all models (harder for some languages than others, but still a lot of manual work meant to be done by generators).

/cc @brjohnstmsft

[ghost]

Thanks for the feedback! We are routing this to the appropriate team for follow-up. cc @felixwa, @brjohnstmsft.

[heaths]

We'll track indivudual items in Azure/azure-rest-api-specs, though I think at some point a top-down review would help to improve docs not only for REST APIs, but the client SDK doc comments as well.