refactor(cocoapods): Use a data class for the source property

When the `source` node contains boolean properties with unquoted values,
such as [1], the deserialization of the source property to a
`Map<String, String>` with KxS fails by default. So, introduce a
dedicated data class to prepare for migrating to KxS and to improve the
readability.

[1]: "source": {
       "git": "https://github.com/AFNetworking/AFNetworking.git",
       "tag": "3.2.1",
       "submodules": true
     }

Signed-off-by: Frank Viernau <frank_viernau@epam.com>

plugins/package-managers/cocoapods/src/main/kotlin/CocoaPods.kt

@@ -159,11 +159,11 @@ class CocoaPods(
     private fun getPackage(id: Identifier, workingDir: File): Package {
         val podspec = getPodspec(id, workingDir) ?: return Package.EMPTY.copy(id = id, purl = id.toPurl())
 
-        val vcs = podspec.source["git"]?.let { url ->
+        val vcs = podspec.source?.git?.let { url ->
             VcsInfo(
                 type = VcsType.GIT,
                 url = url,
-                revision = podspec.source["tag"].orEmpty()
+                revision = podspec.source.tag.orEmpty()
             )
         }.orEmpty()
 
@@ -174,7 +174,7 @@ class CocoaPods(
             description = podspec.summary,
             homepageUrl = podspec.homepage,
             binaryArtifact = RemoteArtifact.EMPTY,
-            sourceArtifact = podspec.source["http"]?.let { RemoteArtifact(it, Hash.NONE) }.orEmpty(),
+            sourceArtifact = podspec.source?.http?.let { RemoteArtifact(it, Hash.NONE) }.orEmpty(),
             vcs = vcs,
             vcsProcessed = processPackageVcs(vcs, podspec.homepage)
         )

plugins/package-managers/cocoapods/src/main/kotlin/Podspec.kt

@@ -38,9 +38,16 @@ internal data class Podspec(
     val license: String = "",
     val summary: String = "",
     val homepage: String = "",
-    val source: Map<String, String> = emptyMap(),
+    val source: Source? = null,
     private val subspecs: List<Podspec> = emptyList()
 ) {
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    data class Source(
+        val git: String? = null,
+        val tag: String? = null,
+        val http: String? = null
+    )
+
     fun withSubspecs(): List<Podspec> {
         val result = mutableListOf<Podspec>()