Creates a new `GdkContentFormats` from the given this.
The given `GdkContentFormatsBuilder` is reset once this function returns; you cannot call this function multiple times on the same this instance.
This function is intended primarily for bindings. C code should use [[email protected]_to_formats].
| this |
a `GdkContentFormats`Builder |
|
the newly created `GdkContentFormats` with all the formats added to this |