Load YangFeatureProviders in mdsal-dom-schema-osgi
YangModuleProvider provides a view into explicitly defined per-module
feature set. These are defined by applications implementing YANG
modules which provide if-feature'd contents and the application does
not support the full feature set.
This patch add the basic smarts to perform loading of providers, and
propagates them to ModuleInfoSnapshotResolver.
JIRA: MDSAL-790
Change-Id: Ib08915be7b5aba785a8a09ec28dd6e008b61db67
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>