title: buildConfigField for collection by reading .properties file
body: <p><a href="https://stackoverflow.com/questions/42130730/gradle-buildconfigfield-syntax-for-arrays-maps">Gradle buildConfigField: Syntax for arrays &amp; maps?</a> post gives hint to generate <code>Dictionary</code>, <code>Set&lt;T&gt;</code>, <code>Collection</code> or <code>HashTable&lt;T&gt;</code> for <code>buildConfigField</code>. </p>
  
  <p>I'd like to know it is possible to load <code>.properties</code> file and generates a collection variable as <code>BuildConfig</code> variables.</p>
  
  <p><strong>dev.properties</strong></p>
  
  <pre><code>Variable1 = 'some'
  Variable2 = 'value'
  </code></pre>
  
  <p><strong>app.gradle</strong></p>
  
  <pre><code>ext {
      // Read properties file
      Properties devProperty = new Properties()
      def devPropertyFile = file(getRootDir().getPath() + File.separator + 'dev.properties')
      try {
          devProperty.load(new FileInputStream(devPropertyFile))
      } catch (FileNotFoundException e) {
          devProperty = null
          System.out.println('devProperty is null')
      }
  
      // Read property field names as a String set
      Set&lt;String&gt; devSet = devProperty?.stringPropertyNames()
  }
  
  
  android {
      ...
      defaultConfig {
          // Below trial gives error
          buildConfigField 'java.util.Set&lt;String&gt;', 'PropertyNames', project.devSet
      }
  }
  </code></pre>
  
  <p><strong>Expected result 1</strong></p>
  
  <p>By accessing <code>BuildConfig.devSet</code> in java code has <code>["Variable1, Variable2"]</code> values.</p>
  
  <p><strong>Expected result 2</strong></p>
  
  <p>It would be good to access <code>Properties devProperty</code> itself in application code as below;</p>
  
  <p><code>String var1 = BuildConfig.devProperty["Variable1"];</code></p>