cmPackageInfoReader: Inherit cps_version

Modify cmPackageInfoReader to not require schema_version in supplemental
files (i.e. appendices and/or configuration-specific files). This is
important as our own generation is not including cps_version in
supplemental files, and it is forbidden in the same according to a
strict reading of the specification.

Source/cmPackageInfoReader.cxx

@@ -376,7 +376,7 @@ std::unique_ptr<cmPackageInfoReader> cmPackageInfoReader::Read(
   //   - the input is a JSON object
   //   - the input has a "cps_version" that we (in theory) know how to parse
   Json::Value data = ReadJson(path);
-  if (!data.isObject() || !CheckSchemaVersion(data)) {
+  if (!data.isObject() || (!parent && !CheckSchemaVersion(data))) {
     return nullptr;
   }
 

Tests/FindPackageCpsTest/cps/foo-relative@default.cps

@@ -1,5 +1,4 @@
 {
-  "cps_version": "0.13",
   "name": "Foo",
   "configuration": "default",
   "components": {