[Blob] Design for enabling inference of collection binding without the IsBatched property

[jviau]

Using blob extension as an example:

We should explore if we can remove the need for the explicit IsBatched value in BlobInputAttribute and instead infer it on some set of defined rules. This may be possible by both considering the target parameter type as well is if the described blob is a file or not. We will need to explore how this affects binding metadata sent to/from the host.

Examples

Is File?	Target Type	Result
true	IEnumerable<T>, Array<T>	deserialize single file into target type, Behavior of deserialization depends on how the configured serializer performs collection deserialization.
true	T (not an enumerable or array)	deserialize single file into target type.
true	string, Stream, byte[]	blob contents. The check for byte[] will need to take precedence over the array check above.
true	BlobClient	provide BlobClient for described blob
true	IEnumerable<BlobClient> / Array<BlobClient>	enumerable/array with single client
true	BlobContainerClient	error (need to verify this)
true	IEnumerable<BlobContainerClient> / Array<BlobContainerClient>	error (need to verify this)
false	IEnumerable<T>, Array<T>	deserialize single file into target type, Behavior of deserialization depends on how the configured serializer performs collection deserialization.
false	T (not an enumerable or array)	error
false	string, Stream, byte[]	error
false	BlobClient	provide BlobClient for indicated blob (IsFile will be false - this does work today).
false	IEnumerable<BlobClient> / Array<BlobClient>	enumerable/array with a BlobClient per child.
false	BlobContainerClient	provide BlobContainerClient for the indicated blob.
false	IEnumerable<BlobContainerClient> / Array<BlobContainerClient>	enumerable / array with single BlobContainerClient. Or error? There is never a case this would yield more than 1.