feat(PurlUtils): Add optional parameters to toPurl

The commit 7da5ae9 changed the visibility of `createPurl`, `toPurl` has
become the only public ORT function for plugins to generate Purls.
Since this function does not support qualifiers nor subpath, these two
parameters have to be added to the function signature with default values.

The `JvmOverloads` annotation is used to make this function with default
parameters compatible with calls coming from FreeMarker templates.

Signed-off-by: Nicolas Nobelis <[email protected]>

model/src/main/kotlin/utils/PurlUtils.kt

@@ -86,12 +86,18 @@ fun Identifier.getPurlType() =
  * Create the canonical [package URL](https://github.com/package-url/purl-spec) ("purl") based on the properties of
  * the [Identifier]. Some issues remain with this specification
  * (see e.g. https://github.com/package-url/purl-spec/issues/33).
+ * Optional [qualifiers] may be given and will be appended to the purl as query parameters e.g.
+ * pkg:deb/debian/[email protected]?arch=i386&distro=jessie
+ * Optional [subpath] may be given and will be appended to the purl e.g.
+ * pkg:golang/google.golang.org/genproto#googleapis/api/annotations
  *
  * This implementation uses the package type as 'type' purl element as it is used
  * [in the documentation](https://github.com/package-url/purl-spec/blob/master/README.rst#purl).
  * E.g. 'maven' for Gradle projects.
  */
-fun Identifier.toPurl() = if (this == Identifier.EMPTY) "" else createPurl(getPurlType(), namespace, name, version)
+@JvmOverloads
+fun Identifier.toPurl(qualifiers: Map<String, String> = emptyMap(), subpath: String = "") =
+    if (this == Identifier.EMPTY) "" else createPurl(getPurlType(), namespace, name, version, qualifiers, subpath)
 
 /**
  * Create the canonical [package URL](https://github.com/package-url/purl-spec) ("purl") based on given properties: