- #73 - implement a few of the missing features

[kirides]

This PR implements the following features

• SQLiteWriteOnlyTransaction.AcquireDistributedLock (Transaction.AcquireDistributedLock)
• HangfireSQLiteConnection.GetSetCount-Limited (Connection.GetSetCount.Limited)
• HangfireSQLiteConnection.GetSetContains (Connection.GetSetContains)
• HangfireSQLiteConnection.GetFirstByLowestScoreFromSet (Connection.BatchedGetFirstByLowestScoreFromSet)
• HangfireSQLiteConnection.GetUtcDateTime (Connection.GetUtcDateTime)

and ignores an ObjectDisposedException when the Heartbeat timer already got disposed while being fired

Feature diff is

{ "Storage.ExtendedApi", false },                            -> true
{ "Job.Queue", true },
{ "Connection.GetUtcDateTime", false },                      -> true
{ "Connection.BatchedGetFirstByLowestScoreFromSet", false }, -> true
{ "Connection.GetSetContains", true },                       -> true, was not implemented before, but marked as true
{ "Connection.GetSetCount.Limited", false },                 -> true
{ "BatchedGetFirstByLowestScoreFromSet", false },            -> true
{ "Transaction.AcquireDistributedLock", true },              -> true, was not implemented before, but marked as true
{ "Transaction.CreateJob", true },                           -> false, is not implemented, we should not advertise it
{ "Transaction.SetJobParameter", true },                     -> false, is not implemented, we should not advertise it
{ "TransactionalAcknowledge:InMemoryFetchedJob", false },
{ "Monitoring.DeletedStateGraphs", false },
{ "Monitoring.AwaitingJobs", false }

Addtionally:

• introduced SqliteInMemoryTestBase to simplify correct usage of in-memory database
  • as in-memory databases get deleted once their last connection is "closed", we should always ensure that a test keeps the database alive until its finished, no matter how often the newly created connections get closed.
• improve performance when acquiring connections, by only migrating the tables on the creation of the storage
• reduced allocations by making use of TState-parameter introduced in TryFewTimesDueToConcurrency
• replace manual SQLITE_OPEN_URI-constant with SQLitePCL.raw.SQLITE_OPEN_URI

[kirides]

@felixclase i added a bit more to this PR while i looked around the code

If that makes the PR too big, feel free to say so and i will rever the additional changes and open another PR if this one gets merged.

[kirides]

please don't mind the force pushes, i mistakenly used the wrong git-information in the previous commits.
The new ones are properly signed-off again