resolve: rename {status} to {mergestatus} to not shadow change status (BC)

This is a part of the name unification. I think it's somewhat useful to
provide a combined view of change/merge statuses.

https://www.mercurial-scm.org/wiki/GenericTemplatingPlan#Dictionary

mercurial/commands.py

@@ -4622,7 +4622,7 b' def resolve(ui, repo, *pats, **opts):'
             label, key = mergestateinfo[ms[f]]
             fm.startitem()
             fm.context(ctx=wctx)
-            fm.condwrite(not nostatus, 'status', '%s ', key, label=label)
+            fm.condwrite(not nostatus, 'mergestatus', '%s ', key, label=label)
             fm.write('path', '%s\n', f, label=label)
         fm.end()
         return 0

tests/test-resolve.t

@@ -156,18 +156,18 b' resolve -l should show resolved file as '
   $ hg resolve -l -Tjson
   [
    {
-    "path": "file1",
-    "status": "R"
+    "mergestatus": "R",
+    "path": "file1"
    },
    {
-    "path": "file2",
-    "status": "U"
+    "mergestatus": "U",
+    "path": "file2"
    }
   ]
 
-  $ hg resolve -l -T '{path} {status} {p1rev} {p2rev}\n'
-  file1 R 2 1
-  file2 U 2 1
+  $ hg resolve -l -T '{path} {mergestatus} {status} {p1rev} {p2rev}\n'
+  file1 R M 2 1
+  file2 U M 2 1
 
 resolve -m without paths should mark all resolved