Prior to this change, VersionResourceResolver and VersionStrategy would
resolve static resources using version strings. They assist
ResourceHttpRequestHandler with serving static resources. The
RequestHandler itself can be configured with HTTP caching strategies to
set Cache-Control headers.
In order to have a complete strategy with Cache-Control and ETag
response headers, developers can't reuse that version string information
and have to rely on other mechanisms (like ShallowEtagHeaderFilter).
This commit makes VersionResourceResolver use that version string to set
it as a request attribute, which will be used by the
ResourceHttpRequestHandler to write an ETag response header.
Issue: SPR-13382
190eb6ace1