Issue #2266 Rework Scanner and use it for Jetty Maven Plugin

[janbartel]

Initial bug report: #2266
Problem diagnosis with PathWatcher class here: #4221

It is easier to rework the Scanner class a little to use Paths than to fathom how to fix the PathWatcher class. As this is jetty-9.4.x I've kept the old Scanner api methods, but deprecated them in favour of new Path-based methods. Scanner can be further cleaned up when it is merged through to jetty-10.

[joakime]

I'll test these changes on Microsoft Windows and OSX tomorrow.

[joakime]

I'll rerun the OSX and Windows tests on this PR in the morning.
So far, the prior runs were problematic on OSX (lots of test failures)

OSX Failures:

org.opentest4j.AssertionFailedError: Contexts.size ==> expected: <1> but was: <2>
	at org.eclipse.jetty.deploy.providers.ScanningAppProviderRuntimeUpdatesTest.testAfterStartupThenRemoveContext(ScanningAppProviderRuntimeUpdatesTest.java:146)

org.opentest4j.AssertionFailedError: Contexts.size ==> expected: <1> but was: <2>
	at org.eclipse.jetty.deploy.providers.ScanningAppProviderRuntimeUpdatesTest.testAfterStartupThenUpdateContext(ScanningAppProviderRuntimeUpdatesTest.java:173)

org.opentest4j.AssertionFailedError: Contexts.size ==> expected: <1> but was: <2>
	at org.eclipse.jetty.deploy.providers.ScanningAppProviderRuntimeUpdatesTest.testAfterStartupContext(ScanningAppProviderRuntimeUpdatesTest.java:129)

org.opentest4j.AssertionFailedError: Contexts.size ==> expected: <1> but was: <2>
	at org.eclipse.jetty.deploy.providers.ScanningAppProviderStartupTest.testStartupContext(ScanningAppProviderStartupTest.java:68)

 org.eclipse.jetty.maven.its.jetty-cdi-run-forked.jetty-cdi-run-forked
The post-build script did not succeed. assert buildLog.text.contains( 'helloServlet')

org.eclipse.jetty.maven.its.jetty-run-forked-mojo-it.jetty-run-forked-mojo-it
The post-build script did not succeed. assert buildLog.text.contains( 'pingServlet ok')

[janbartel]

@joakime please make sure you're running the most recent checkin - 99f15cd

That's the most recent fixes.

[janbartel]

@gregw please re-review.

[joakime]

LGTM.
OSX isn't complaining.
I have a dead Windows machine ATM, so I cannot test on Windows until I get it fixed or replaced.