client/x11: Enhance Xutf8TextListToTextProperty
client/x11: Enhance Xutf8TextListToTextProperty

XCompoundTextStyle depends on the current locale and some locales fail
to to get the compound text style.
If Xutf8TextListToTextProperty() fails, now ibus-x11 tries to get
the compound text style with UTF-8 encoding.

BUG=https://github.com/ibus/ibus/issues/2422

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