Support Shadow element selector

// zul file
<div id="div">
    <apply id="sh1">
          <if test="true">
                <label value="I am here"/>
          </if>
    </apply>
</div>

List<Component> applies = Selectors.find(page, "::shadow #sh1");

// or
List<Component> ifs = Selectors.find(page, ":host(#div)::shadow if");

#div::shadow if > label

// the user should use the following way instead
#div > label

::shadow pseudo element
/deep/ combinator, which was replaced with a >>> combinator (or shadow piercing descendant combinator)
::content pseudo-element
:host pseudo-class and :host() functional pseudo-class
:host-context() functional pseudo-class