This commits adds a few common flags to `SocketDeclaration`
so that they are available for all socket types (hide label, hide
value, is multi input). This allows porting over the remaining
geometry nodes to the new declaration system.
Furthermore, this commit separates the concepts of the socket
declaration and corresponding builders. The builders are used
by nodes to declare which sockets they have (e.g. `FloatBuilder`).
The ready build socket declarations can then be consumed by
other systems such as the versioning code. Both use cases
need different APIs and those will change for independent reasons,
so it makes sense to separate the classes.
Previously, built-in nodes had to implement "socket templates"
(`bNodeSocketTemplate`) to tell Blender which sockets they have.
It was nice that this was declarative, but this approach was way
too rigid and was cumbersome to use in many cases.
This commit starts to move us away from this rigid structure
by letting nodes implement a function that declares the sockets
the node has. Right now this is used as a direct replacement
of the "socket template" approach to keep the refactor smaller.
It's just a bit easier to read and write.
In the future we want to support more complex features like
dynamic numbers of sockets and type inferencing. Those features
will be easier to build on this new approach.
This new approach can live side by side with `bNodeSocketTemplate`
for a while. That makes it easier to update nodes one by one.
Note: In `bNodeSocketTemplate` socket identifiers were made
unique automatically. In this new approach, one has to specify
unique identifiers manually (unless the name is unique already).
Differential Revision: https://developer.blender.org/D12335
