[GLib] Add filesystem GType registration mechanism #51816

Describe the enhancement requested

Parent issue: #51608

As part of splitting the S3 GLib bindings into arrow-s3-glib, arrow-glib needs a generic way for filesystem implementations to register their corresponding GType.

Tasks

• Add a filesystem GType registration mechanism.
• Update garrow_file_system_new_raw() to look up the registered GType for a filesystem.
• Fall back to GArrowFileSystem when no matching GType is registered.
• Add tests for the registration, lookup, and fallback behavior.

The exact API name/signature for the registration mechanism can be decided as part of this issue. garrow_file_system_register_type(type_name, gtype) was proposed in #51608.

Component(s)

GLib