flagutil: move REVIDX_KNOWN_FLAGS source of truth in flagutil (API) Since REVIDX_KNOWN_FLAGS is "not really a constant" (extension can update it) and python integer,... it needs to be the responsability of a single module and always accessed through the module. We update all the user and move the source of truth in flagutil.

flagutil: move the `flagprocessors` mapping in the new module This module is meant to host most of the flag processing logic. We start with the mapping between flag and processors.

flagutil: create a `mercurial.revlogutils.flagutil` module The flagprocessings logic is duplicated in 2 extra places, and usually in a less robust flavor. This is a maintenance nightmare that I would like to see cleaned up. To do so I am creating a `flagutil` module to move flag processings related code and make it easily reusable by other code.

rawdata: register the method for `ifiledata` The interface have a `revision(..., raw=False)` method so it should get a `rawdata` one. I am not sure why nothing complained about the lack of it earlier.

rawdata: implement the method for `unionrepo` too This is required for all implementations.

rawdata: implement the method for `remotefilelog` too This is needed for all storage implementations.

rawdata: implement `rawdata` for `simplestore` too This is needed for all implementation.

rawdata: forward `rawdata` call on `manifestlog` This needs to be sent to the underlying `revlog` too.

rawdata: implement `rawdata` for `sqlitestore` too This is a different store, it needs it declared.

rawdata: add the method to bundlerevlog The bundlerepo logic has its own `revision` method on its own `revlog` object. We need to "implement" `rawdata` there too.