Update HazelcastInstance.getCache return type to allow proxying

[vbekiaris]

Avoid ClassNotFoundException when JCache is not in the classpath and HazelcastInstance is proxied (eg. when mocking with Mockito, instantiating as Spring bean).
In a separate commit, added a convenience method in CacheUtil that returns the distributed object name for the given cache, which can be used to obtain an ICache reference from HazelcastInstance.getDistributedObject.
Fixes #8352

[devOpsHazelcast]

Test FAILed.

[devOpsHazelcast]

Test PASSed.

[serkan-ozal]

Regarding to existence of the ICache in the generated byte code:

this is the output of javap -verbose HazelcastInstance.class:

public abstract <C extends java.io.Closeable & com.hazelcast.cache.ICache> C getCache(java.lang.String);
    descriptor: (Ljava/lang/String;)Ljava/io/Closeable;
    flags: ACC_PUBLIC, ACC_ABSTRACT
    Signature: #64                          // <C::Ljava/io/Closeable;:Lcom/hazelcast/cache/ICache;>(Ljava/lang/String;)TC;

Method m = HazelcastInstance.class.getMethod("getCache", String.class);
Type[] returnTypes = ((TypeVariableImpl) m.getGenericReturnType()).getBounds();
for (Type returnType : returnTypes) {
    System.out.println(returnType);
}

prints

interface java.io.Closeable
interface com.hazelcast.cache.ICache