revset-matching: call 'getset' on a 'fullreposet'

Calling 'baseset(repo.changelog)' builds a list for all revisions in
the repo. And we already have the lazy and efficient 'fullreposet'
class for this purpose.

This gives us the usual benefits of the fullreposet but it is less visible
because the matching process itself is very expensive:

revset) matching(100)
before) wall 6.413281 comb 6.420000 user 5.910000 sys 0.510000 (best of 3)
after)  wall 6.173608 comb 6.170000 user 5.750000 sys 0.420000 (best of 3)

However for some complex list, this provide a massive speedup

revset) matching(parents(100))
before) wall 23.890740 comb 23.890000 user 23.450000 sys 0.440000 (best of 3)
after)  wall 6.382280 comb 6.390000 user 5.930000 sys 0.460000 (best of 3)

mercurial/revset.py

@@ -1383,7 +1383,7 b' def matching(repo, subset, x):'
     # i18n: "matching" is a keyword
     l = getargs(x, 1, 2, _("matching takes 1 or 2 arguments"))
 
-    revs = getset(repo, baseset(repo.changelog), l[0])
+    revs = getset(repo, fullreposet(repo), l[0])
 
     fieldlist = ['metadata']
     if len(l) > 1: