The goal here is to make it easier to use the socket declaration builder
for cases where the actual socket type is not known at compile time.
For that purpose, all the methods that are not dependent on the specific
socket type are moved to the base socket declaration builder.
A nice side effect of this is reduced templated boilerplate and that more
code can be moved out of the header.
With this patch, one is now forced to put type specific method calls before
generic method calls in a chain. For example `.default_value(...).supports_field()`
instead of `supports_field().default_value(...)`. In theory, we could keep
support for both orders but that would involve a lot of additional boilerplate
code. Enforcing this order is simple enough. Note that this limitation only
applies when chaining multiple method calls. This is still possible:
```
auto &decl = b.add_input<decl::Vector>("Value");
decl.supports_field();
decl.default_value(...);
```
Pull Request: https://projects.blender.org/blender/blender/pulls/113410
f3a1dd1eb5