* CORDA-939 Modify Api Scanner to check api for internal exposures (#2510)
* Update check api changes to look for internals
* Update several more uses of internal
* Make check-api-changes script filter out internal class usages
* Make CordaClock part of API
* Update api-current.txt
* Remove exclusion of nodeapi.internal
* Remove access to CordaPersistence from public api
* Don't expose DB Connection from StartedMockNode and remove unnecessary transaction from CustomVaultQueryTest
* Make internal tests that use need db access use InternalMockNetwork
* Make test certificates internal
* Address further review comments
* Revert some accidental changes to api-current.txt
* Address Shams' review comments
* Update Api Scanner to filter out CordaInternal attribute
* Update api-current.txt
* Remove superfluous brackets
* Add transaction to StartedMockNode
* More leaky transaction fixes
# Conflicts:
# .ci/api-current.txt
# node-api/src/test/kotlin/net/corda/nodeapi/internal/AttachmentsClassLoaderStaticContractTests.kt
# node-api/src/test/kotlin/net/corda/nodeapi/internal/AttachmentsClassLoaderTests.kt
# node/src/integration-test/kotlin/net/corda/node/services/AttachmentLoadingTests.kt
# node/src/test/kotlin/net/corda/node/internal/cordapp/CordappProviderImplTests.kt
# testing/node-driver/src/main/kotlin/net/corda/testing/node/internal/InternalMockNetwork.kt
# testing/test-utils/src/main/kotlin/net/corda/testing/internal/MockCordappConfigProvider.kt
# testing/test-utils/src/main/kotlin/net/corda/testing/internal/MockCordappProvider.kt
* Bump gradle plugins version
* One last internal exposure
* Update constants.properties
* Fix api-current
* Address mikes review comments
* Enhance the API Scanner plugin to monitor class annotations.
* Implement @DoNotImplement annotation, and apply it.
* Update API definition.
* Update API change detection to handle @DoNotImplement.
* Document the `@DoNotImplement` annotation.
* Scan API for addition of new abstract methods.
* Make sure we ignore blank lines when counting API changes.
* Add 6 new abstract APIs to our API definition.
