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ARROW-6347: [GLib] Add garrow_array_diff()

Closes #5197 from shiro615/glib-diff and squashes the following commits:

dfa11b3a1 <Yosuke Shiro> Use assert_nil for nil check
ed1998902 <Yosuke Shiro> Use 'test_diff' for valid test case name
9fc3eb717 <Yosuke Shiro> Add a description for NULL case
14767b1e7 <Yosuke Shiro> Add a test case for different type arrays
cad4ffdbd <Yosuke Shiro> Add diffrerent type test cases
11330a2ba <Yosuke Shiro> Return NULL when no difference
d16a7f0ee <Yosuke Shiro> Rename garrow_array_diff() to garrow_array_diff_unified()
a41e8c237 <Yosuke Shiro> Use EqualOptions :: diff_sink in garrow_array_diff()
4e6b4ab5e <Yosuke Shiro>  Add garrow_array_diff()

Authored-by: Yosuke Shiro <yosuke.shiro615@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>