/usr/bin/gapi3-parser is in gtk-sharp3-gapi 2.99.3-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 | #!/bin/sh
export PATH=/usr/lib/gapi-3.0:$PATH
mono /usr/lib/gapi-3.0/gapi-parser.exe "$@"
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