ARROW-5307: [CI][GLib] Enable GTK-Doc
ARROW-5307: [CI][GLib] Enable GTK-Doc

> Enable GTK-Doc when 1.31 is released.
>See https://issues.apache.org/jira/browse/ARROW-5306.

GTK-Doc 1.31 was released.

Closes #5087 from shiro615/enable-gtk-doc and squashes the following commits:

d0b7c3744 <Yosuke Shiro>  Enable GTK-Doc

Authored-by: Yosuke Shiro <566f3c030d8064e2a2a198dafd4d52e9d358b1f1@gmail.com>
Signed-off-by: Sutou Kouhei <73218711cdd5d5c30ac66da3cc4d9d9204caf34b@clear-code.com>

xhochy/arrow,xhochy/arrow,renesugar/arrow,renesugar/arrow,xhochy/arrow,icexelloss/arrow,icexelloss/arrow,laurentgo/arrow,xhochy/arrow,wesm/arrow,icexelloss/arrow,apache/arrow,apache/arrow,cpcloud/arrow,cpcloud/arrow,kou/arrow,xhochy/arrow,icexelloss/arrow,icexelloss/arrow,kou/arrow,kou/arrow,kou/arrow,cpcloud/arrow,laurentgo/arrow,wesm/arrow,renesugar/arrow,apache/arrow,xhochy/arrow,xhochy/arrow,apache/arrow,wesm/arrow,apache/arrow,apache/arrow,renesugar/arrow,cpcloud/arrow,apache/arrow,wesm/arrow,kou/arrow,icexelloss/arrow,xhochy/arrow,xhochy/arrow,laurentgo/arrow,wesm/arrow,laurentgo/arrow,xhochy/arrow,wesm/arrow,apache/arrow,cpcloud/arrow,kou/arrow,icexelloss/arrow,icexelloss/arrow,icexelloss/arrow,wesm/arrow,kou/arrow,cpcloud/arrow,laurentgo/arrow,apache/arrow,laurentgo/arrow,kou/arrow,wesm/arrow,icexelloss/arrow,apache/arrow,wesm/arrow,renesugar/arrow,kou/arrow,kou/arrow,xhochy/arrow,apache/arrow,cpcloud/arrow,renesugar/arrow,wesm/arrow,wesm/arrow,renesugar/arrow,renesugar/arrow,kou/arrow,laurentgo/arrow,cpcloud/arrow,renesugar/arrow,kou/arrow,renesugar/arrow,renesugar/arrow,cpcloud/arrow,wesm/arrow,xhochy/arrow,renesugar/arrow,kou/arrow,icexelloss/arrow,laurentgo/arrow,wesm/arrow,icexelloss/arrow,apache/arrow,cpcloud/arrow,renesugar/arrow,kou/arrow,laurentgo/arrow,apache/arrow,icexelloss/arrow,icexelloss/arrow,cpcloud/arrow,laurentgo/arrow,cpcloud/arrow,laurentgo/arrow,cpcloud/arrow,cpcloud/arrow,renesugar/arrow,xhochy/arrow,xhochy/arrow,laurentgo/arrow,laurentgo/arrow,wesm/arrow,renesugar/arrow,laurentgo/arrow,apache/arrow,xhochy/arrow,laurentgo/arrow