* Instantiating the contract class should be part of contract verification. We should not instantiate it while building LedgerTransaction.
* Also catch any exceptions from instantiating the contract.
* Making Corda's JPA classes non-final and Serializable.
* Making Corda's JPA classes non-final and Serializable.
* Making Corda's JPA classes non-final and Serializable.
* Making Corda's JPA classes non-final and Serializable.
* ENT-1670: update kdocs and unit test for better user experience regarding
RPC connection loss
* RPCStabilityTests: move doOnError logic to onError handler
Problem manifests now that the classpath scanner is used by the
serialisation framework in factory initialization to locate pluggable
serializers. The actual thrown error is
java.lang.RuntimeException: Unknown constant pool tag
Given this is a known issue and a fixed bug it makes sense to move the
version forward. Unfortunately at this time we cannot move beyond
2.12.3 as 2.12.4 and later versions (up to the latest 2.18.1) exhibit
some other error that needs investigating. Thus, move to the latest
version that is stable for our current set of use cases.
More information on the nature of the problem exhibited by moving beyond
2.12.3 can be found on the linked Jira (ENT-1665) as well as details on
reproducing the issue moving forward to 2.12.3 fixes.
Prior to this change it was intermittently failing with:
```
net.corda.client.rpc.RPCException: RPC server is not available.
at net.corda.client.rpc.internal.RPCClientProxyHandler.invoke(RPCClientProxyHandler.kt:222)
at com.sun.proxy.$Proxy79.ping(Unknown Source)
at net.corda.client.rpc.RPCStabilityTests$client reconnects to rebooted server$1$pingFuture$1.invoke(RPCStabilityTests.kt:251)
at net.corda.client.rpc.RPCStabilityTests$client reconnects to rebooted server$1$pingFuture$1.invoke(RPCStabilityTests.kt:36)
at net.corda.core.internal.concurrent.ValueOrException$DefaultImpls.capture(CordaFutureImpl.kt:107)
at net.corda.core.internal.concurrent.OpenFuture$DefaultImpls.capture(CordaFutureImpl.kt:65535)
at net.corda.core.internal.concurrent.CordaFutureImpl.capture(CordaFutureImpl.kt:119)
at net.corda.core.internal.concurrent.CordaFutureImplKt$fork$$inlined$also$lambda$1.run(CordaFutureImpl.kt:22)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:748)
```
