Ignore "Unknown referenced nature" warnings

[fbricon]

Eclipse projects opened/configured in Eclipse might have natures that are not necessarily available in jdt.ls, like for WTP projects typically, and they produce warnings like:

See .project:

<?xml version="1.0" encoding="UTF-8"?>
<projectDescription>
	<name>multi-web</name>
	<comment></comment>
	<projects>
	</projects>
	<buildSpec>
		<buildCommand>
			<name>org.eclipse.jdt.core.javabuilder</name>
			<arguments>
			</arguments>
		</buildCommand>
		<buildCommand>
			<name>org.eclipse.wst.common.project.facet.core.builder</name>
			<arguments>
			</arguments>
		</buildCommand>
		<buildCommand>
			<name>org.eclipse.wst.validation.validationbuilder</name>
			<arguments>
			</arguments>
		</buildCommand>
		<buildCommand>
			<name>org.eclipse.m2e.core.maven2Builder</name>
			<arguments>
			</arguments>
		</buildCommand>
	</buildSpec>
	<natures>
		<nature>org.eclipse.jem.workbench.JavaEMFNature</nature>
		<nature>org.eclipse.wst.common.modulecore.ModuleCoreNature</nature>
		<nature>org.eclipse.jdt.core.javanature</nature>
		<nature>org.eclipse.m2e.core.maven2Nature</nature>
		<nature>org.eclipse.wst.common.project.facet.core.nature</nature>
		<nature>org.eclipse.wst.jsdt.core.jsNature</nature>
	</natures>
</projectDescription>

We should simply ignore those warnings.