Adding PolicySet parsePolicies method

[mark-creamer-amazon]

#38

CedarJava

• Added static PolicySet parsePolicies(Path filePath) and PolicySet parsePolicies(String policiesString) methods to PolicySet.
• Added PolicySetTests file that tests the File path and string methods and some exception cases.
• Adding test cedar policy files in src/test/resources directory to use for testing.

CedarJavaFFI

• Added JNI method parsePoliciesJni that takes a Java String for policies and templates, uses PolicySet::from_str to parse the string into policies and templates and then constructs a Java PolicySet with those parameters. Template instantiations are omitted.

[khieta]

Looking good! Could you also update the integration tests to use these new APIs instead of hacky splitting on semicolons? Relevant code is here:

cedar-java/CedarJava/src/test/java/com/cedarpolicy/SharedIntegrationTests.java

Line 284 in 8baec5e

private Set<Policy> loadPolicies(String policiesFile) throws IOException {

[khieta]

Lgtm