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-commandserver.t	Wed Oct 21 19:00:16 2020 -0700
+++ b/tests/test-commandserver.t	Tue Oct 06 22:36:15 2020 -0700
@@ -714,7 +714,7 @@
   o, 'capabilities: getencoding runcommand\nencoding: *\npid: *' (glob)
   *** runcommand id
   abort: there is no Mercurial repository here (.hg not found)
-   [255]
+   [10]
 
   >>> from hgclient import check, readchannel, runcommand
   >>> @check