revlog: use raw revision for rawsize

When writing the revlog-ng index, the third field is len(rawtext). See
revlog._addrevision:

    textlen = len(rawtext)
    ....
    e = (offset_type(offset, flags), l, textlen,
         base, link, p1r, p2r, node)
    self.index.insert(-1, e)

Therefore, revlog.index[rev][2] returned by revlog.rawsize should be
len(rawtext), where "rawtext" is revlog.revision(raw=True).

Unfortunately it's hard to add a test for this code path because "if l >= 0"
catches most cases.

mercurial/revlog.py

@@ -444,7 +444,7 b' class revlog(object):'
         if l >= 0:
             return l
 
-        t = self.revision(rev)
+        t = self.revision(rev, raw=True)
         return len(t)
     size = rawsize