title: gradle fileTree with variable dir
body: <p>I am not sure if this is supported by fileTree. I searched the document and all examples used concrete (absolute or relative) paths.  This is what I want to do.</p>
  
  <pre><code>ext {
      externalProjectRoot "c:/AnotherProject"
  }
  
  implementation fileTree(dir: ${externalProjectRoot}/lib', include: '*.jar')
  </code></pre>
  
  <p>If I do the following, it works.</p>
  
  <pre><code>implementation fileTree(dir: 'c:/AnotherProject/lib', include: '*.jar')
  </code></pre>
  
  <p>So I suspect that the fileTree function doesn't support variable for the dir attribute.  If not, what other options do I have?</p>
  
  <p>Thanks!</p>