errors: introduce InputError and use it from commands and cmdutil This patch introduces a `InputError` class and replaces many uses of `error.Abort` by it in `commands` and `cmdutil`. This is a part of https://www.mercurial-scm.org/wiki/ErrorCategoriesPlan. There will later be a different class for state errors (to raise e.g. when there's an unfinished operation). It's not always clear when one should report an input error and when it should be a state error. We can always adjust later if I got something wrong in this patch (but feel free to point out any you notice now). Differential Revision: https://phab.mercurial-scm.org/D9167

--- a/tests/test-uncommit.t	Wed Oct 21 19:00:16 2020 -0700
+++ b/tests/test-uncommit.t	Tue Oct 06 22:36:15 2020 -0700
@@ -556,10 +556,10 @@
   $ hg rollback -q --config ui.rollback=True
   $ hg uncommit -U --user 'user'
   abort: cannot specify both --user and --currentuser
-  [255]
+  [10]
   $ hg uncommit -D --date today
   abort: cannot specify both --date and --currentdate
-  [255]
+  [10]
 
 `uncommit <dir>` and `cd <dir> && uncommit .` behave the same...