templater: adjust binding strength of '%' and '|' operators (BC)

This makes 'foo|bar%baz' parsed as '(foo|bar)%baz', not 'foo|(bar%baz)'.
Perhaps it was a mistake that '%' preceded '|'. Both '|' and '%' can be
considered a kind of function application, and '|' is more like a '.' operator
seen in OO languages. So IMHO '|' should have the same (or higher) binding as
'%'.

The BC breakage should be minimal since both '|' and '%' operators have
strict requirements for their operands and 'foo|bar%baz' was invalid:

 - right-hand side of '|' must be a symbol
 - left-hand side of '%' must be a dict or list
 - right-hand side of '%' must be a string or symbol

mercurial/templater.py

@@ -34,7 +34,7 b' from . import ('
 elements = {
     # token-type: binding-strength, primary, prefix, infix, suffix
     "(": (20, None, ("group", 1, ")"), ("func", 1, ")"), None),
-    "%": (16, None, None, ("%", 16), None),
+    "%": (15, None, None, ("%", 15), None),
     "|": (15, None, None, ("|", 15), None),
     "*": (5, None, None, ("*", 5), None),
     "/": (5, None, None, ("/", 5), None),

tests/test-command-template.t

@@ -134,6 +134,20 b' But negate binds closer still:'
     (string '\n'))
   -3
 
+Filters bind as close as map operator:
+
+  $ hg debugtemplate -r0 -v '{desc|splitlines % "{line}\n"}'
+  (template
+    (%
+      (|
+        (symbol 'desc')
+        (symbol 'splitlines'))
+      (template
+        (symbol 'line')
+        (string '\n'))))
+  line 1
+  line 2
+
 Keyword arguments:
 
   $ hg debugtemplate -r0 -v '{foo=bar|baz}'