formats mappings adjustments (breaking batch)

[baywet]

While working on documenting the different format that can be used in OAS I realized Kiota was not mapping some formats properly:

• "decimal" should only be a child of string type as the serialization process will trim trailing zeros for numbers, loosing precision. => map string:decimal to a string (decimal type) on the wire, and number:decimal to a number (double) on the wire. (BREAKING)
• "base64" and "base64url" are different in their serialization and deserialization logic, and should ultimately map to stream. (BREAKING)
• should we add support for char? (BREAKING)
• type array with uniqueItems: true (items) should map to a hashset

[baywet]

Currently kiota only support OAS 3.0:

• https://datatracker.ietf.org/doc/html/draft-wright-json-schema-validation-00
• https://github.com/OAI/OpenAPI-Specification/blob/main/versions/3.0.3.md#data-types

Course of action:

• create a separate issue to fix number/float64, binary, byte BEFORE GA (number won't impact dotnet GA as conversion is always adding format)
• move this one to v2 as the rest depends on OAS 3.1

[baywet]

@darrelmiller fixing this one will require coordinating all the abstractions and serialization libs on top of changing the generation. I'd recommend pushing it to v3