class CreateBufferCollectionTokenGroup

Create a logical OR among a set of tokens, called a

[`fuchsia.sysmem2/BufferCollectionTokenGroup`].

Most sysmem clients and many participants don't need to care about this

message or about `BufferCollectionTokenGroup`(s). However, in some cases

a participant wants to attempt to include one set of delegate

participants, but if constraints don't combine successfully that way,

fall back to a different (possibly overlapping) set of delegate

participants, and/or fall back to a less demanding strategy (in terms of

how strict the [`fuchisa.sysmem2/BufferCollectionConstraints`] are,

across all involved delegate participants). In such cases, a

`BufferCollectionTokenGroup` is useful.

A `BufferCollectionTokenGroup` is used to create a 1 of N OR among N

child [`fuchsia.sysmem2/BufferCollectionToken`](s). The child tokens

which are not selected during aggregation will fail (close), which a

potential participant should notice when their `BufferCollection`

channel client endpoint sees PEER_CLOSED, allowing the participant to

clean up the speculative usage that didn't end up happening (this is

simimlar to a normal `BufferCollection` server end closing on failure to

allocate a logical buffer collection or later async failure of a buffer

collection).

See comments on protocol `BufferCollectionTokenGroup`.

Any `rights_attenuation_mask` or `AttachToken`/`SetDispensable` to be

applied to the whole group can be achieved with a

`BufferCollectionToken` for this purpose as a direct parent of the

`BufferCollectionTokenGroup`.

All table fields are currently required.

+ request `group_request` The server end of a

`BufferCollectionTokenGroup` channel to be served by sysmem.