The @value will have been initialized to the GType the value should be
provided in. This given GType does not need to be listed in the formats
returned by [method@Gdk.ContentProvider.ref_formats]. However, if the
given GType is not supported, this operation can fail and
#G_IO_ERROR_NOT_SUPPORTED will be reported.
Gets the contents of @provider stored in @value.
The @value will have been initialized to the GType the value should be provided in. This given GType does not need to be listed in the formats returned by [method@Gdk.ContentProvider.ref_formats]. However, if the given GType is not supported, this operation can fail and #G_IO_ERROR_NOT_SUPPORTED will be reported.