Added InferDictionariesFromRecords flag to JSON TP

[nikoyak]

JSON TP always projects json record fields into the properties
of generated types. Sometimes it is not desirable. The added
flag will allow to infer dictionaries from the records if the names
of all the fields of similar records in the provider's training data
are inferred to the same non-string primitive type (by type inference
rules). The flag is not set by default for backwards compatibility.

The current implementation makes it meaningless to process such data in the JSON Provider:

{ "sales": { "2022-01-13": { "count": 3 }, "2022-01-23": { "count": 5 }, "2022-01-28": { "count": 4 }, "2022-02-01": { "count": 5 }, "2022-02-07": { "count": 1 }, "2022-02-13": { "count": 2 } } }

With this PR, for example, it is easy to find out from the above data how many sales were in February:

type TP = JsonProvider<"""{ "sales": { "1970-01-01": { "count": 100 }}}""", InferDictionariesFromRecords = true>
let s = """{ "sales": { "2022-01-13": { "count": 3 }, "2022-01-23": { "count": 5 }, "2022-01-28": { "count": 4 }, "2022-02-01": { "count": 5 }, "2022-02-07": { "count": 1 }, "2022-02-13": { "count": 2 } } }"""
TP.Parse(s).Sales.Items
|> Seq.filter (fun (k, _) -> k.Month = 2)
|> Seq.sumBy (fun (_, v) -> v.Count)

In addition to the Items: (InferedKey * InferedValue) seq property specified in the code above, the generated dictionary-like type contains the Count, IsEmpty, Keys, Values properties, the Item indexed property, and the ContainsKey, TryFind methods, similar to the members of FSharp.Collections.Map

[cartermp]

Took a look, I think this is a great feature to add. Code looks reasonable.

I'd like to spend a little time mulling it over, though. @dsyme would like to get your take as well.

[dsyme]

Suggest PreferDictionaries instead of InferDictionariesFromRecords

[dsyme]

I left a couple of suggestions, but otherwise marked as approved, the code looks great

[nikoyak]

done

[cartermp]

Thanks!