Add MANIFEST entries to support Liferay's OSGi container

[vaadin-bot]

Originally by sammso

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Add MANIFEST entries to support Liferay 7's OSGi container.

At least following entries should be added.

javax.portlet;version="[2.0,3)";resolution:=optional
javax.portlet.filter;version="[2.0,3)";resolution:=optional
com.liferay.portal.kernel.util;resolution:=optional

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Imported from https://dev.vaadin.com/ issue #18561

[vaadin-bot]

Originally by @hesara

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Adding these should be easy, but one thing we need to check first: does it cause complications when Vaadin is used via p2 (e.g. in Eclipse plug-ins) - see https://chamibuddhika.wordpress.com/2011/06/04/dangers-of-resolutionoptional/ .

[vaadin-bot]

Originally by sammso

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Liferay's point of view import entries does not have be optional.

I did test this with 7.5.1

sammso@2746f9b

[vaadin-bot]

Originally by @hesara

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My point was that "optional" (which is logically correct here) is not "optional enough" in some cases, as p2 by default also bundles some optional dependencies. This is really a p2 problem rather than an OSGi problem. However, after discussing this with John, it looks like optional is ok so we can add these and then make changes to our tycho/p2 builds if it causes problems.

[vaadin-bot]

Originally by @hesara

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Change waiting for review: https://dev.vaadin.com/review/#/c/11764/