Introduce ResourceLoaderLessVarFileModule

Introduce ResourceLoaderLessVarFileModule

This ResourceLoader module provides a way to ship
messages to CSS variables.

We will need this going forward to deal with flash of
unstyled content in various JavaScript based UIs that
are subject to i18n such as table sorting and
collapsible elements.

To avoid overhead of hitting the database to fetch and
transform localisation messages we make use of the MessageBlobStore
making use of `messages` definition already inside
ResourceLoaderFileModule. Given this resource is only intended
for render blocking styles without JavaScript this should be okay
(although if requested in JavaScript will also ship associated
messages)

Bug: T42812
Change-Id: I2bf12cdc848478889acbe9a7a970e46f8aefa287