* GH-3554: Eval remote dir on each synchToLocal
Fixes https://github.com/spring-projects/spring-integration/issues/3554
The `remoteDirectoryExpression` was introduced into an
`AbstractInboundFileSynchronizer` to let end-user to evaluate a remote directory
on each poll (essentially on each `synchronizeToLocalDirectory()` call).
The fix for the https://jira.spring.io/browse/INT-4491 introduced a regression
when such an expression was evaluated only once when we call a `setRemoteDirectory()`.
So, an original purpose of this option was lost and we don't get an actual
remote dir on each poll
* Remove `evaluateRemoteDirectory()` method and its usage since it doesn't
reflect expectation of the remote dir expression property
* Reinstate the `remoteDirectoryExpression` evaluation in the
`synchronizeToLocalDirectory()`
* Propagate the result of that expression into further methods for copying
files
* Remove setting of the `remoteDirectory` variable into a global `EvaluationContext`
of the `AbstractInboundFileSynchronizer` instance since it is not thread-safe
* Instead create an `EvaluationContext` locally for each `synchronizeToLocalDirectory()`
call and set the `remoteDirectory` variable into this scoped instances
* Generate a local file name from the `localFilenameGeneratorExpression`
against locally created `EvaluationContext` with the mentioned `remoteDirectory` variable
* Cover the expected functionality with a unit-test
**Cherry-pick to `5.4.x` & `5.3.x`**
* * Fix `testRemoteDirectoryRefreshedOnEachSynchronization` according PR review
e643477dfb