Allow loading of FormatterProperties from resource

[philipp94831]

Currently it is only possible to load FormatterProperties from a File (e.g., XML in the case of eclipse) or String-based properties (https://github.com/diffplug/spotless/blob/4dd0095437906713fc6bad3a2e160646e11b419a/lib/src/main/java/com/diffplug/spotless/FormatterProperties.java).

However, we would like to ship our XML codestyle definition as a resource file. This cannot be loaded by spotless unless we create a temporary file. Alternatively we would need to manually convert the XML to String-based properties and basically copy the behavior of XMLParser.

Therefore, it would be greate to be able to load FormatterProperties from an input stream (by specifying the file type) or even directly from a resource identifier

[nedtwigg]

For Gradle, I recommend https://github.com/diffplug/blowdryer. I don't know enough about Maven to make any recommendations here.

[rnc]

Maven is straightforward (although it would have been useful to have this in the documentation) :

<plugin>
  <groupId>com.diffplug.spotless</groupId>
  <artifactId>spotless-maven-plugin</artifactId>
  <version>${spotless-maven-plugin.version}</version>
  <dependencies>
    <dependency>
      <groupId>org.jboss.pnc</groupId>
      <artifactId>ide-config</artifactId>
      <version>1.1.0</version>
    </dependency>
  </dependencies>
  <configuration>
    <java>
      <removeUnusedImports/>
      <importOrder>
        <file>java-import-order.txt</file>
      </importOrder>
      <eclipse>
        <file>java-formatter.xml</file>
      </eclipse>
      <lineEndings>UNIX</lineEndings>
    </java>
  </configuration>

For Gradle, while #2343 helped a lot, #2361 might solve your use-case ? (then the resources could be loaded from a resource using a TextResource).