tests: show how `hg split` can put color codes in commit template

With D9255, I made it so `hg split` respects the
`commmand-templates.oneline-summary` config. I don't think I realized
that the output I modified was being put in a commit message
template. The result was that if you have coloring enabled, you get
colors in the commit template. This patch show that. The test is
unfortunately pretty verbose (like most other `hg split` tests) and
shows a bunch of irrelevant "color codes" (templater labels).

Differential Revision: https://phab.mercurial-scm.org/D9321

tests/test-split.t

@@ -976,3 +976,73 b' accidentally.'
   2
   3
   4
+
+Test that color codes don't end up in the commit message template
+----------------------------------------------------
+
+  $ hg init $TESTTMP/colorless
+  $ cd $TESTTMP/colorless
+  $ echo 1 > file1
+  $ echo 1 > file2
+  $ hg ci -qAm initial
+  $ echo 2 > file1
+  $ echo 2 > file2
+  $ cat > $TESTTMP/messages <<EOF
+  > split1, modifying file1
+  > --
+  > split2, modifying file2
+  > EOF
+  $ hg ci
+  EDITOR: 
+  EDITOR: 
+  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
+  EDITOR: HG: Leave message empty to abort commit.
+  EDITOR: HG: --
+  EDITOR: HG: user: test
+  EDITOR: HG: branch 'default'
+  EDITOR: HG: changed file1
+  EDITOR: HG: changed file2
+  $ printf 'f\nn\na\n' | hg split --color=debug \
+  > --config command-templates.oneline-summary='{label("rev", rev)} {desc}'
+  [diff.diffline|diff --git a/file1 b/file1]
+  1 hunks, 1 lines changed
+  [ ui.prompt|examine changes to 'file1'?
+  (enter ? for help) [Ynesfdaq?]] [ ui.promptecho|f]
+  
+  [diff.diffline|diff --git a/file2 b/file2]
+  1 hunks, 1 lines changed
+  [ ui.prompt|examine changes to 'file2'?
+  (enter ? for help) [Ynesfdaq?]] [ ui.promptecho|n]
+  
+  EDITOR: HG: Splitting 6432c65c3078. Write commit message for the first split changeset.
+  EDITOR: split1, modifying file1
+  EDITOR: 
+  EDITOR: 
+  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
+  EDITOR: HG: Leave message empty to abort commit.
+  EDITOR: HG: --
+  EDITOR: HG: user: test
+  EDITOR: HG: branch 'default'
+  EDITOR: HG: changed file1
+  [ ui.status|created new head]
+  [diff.diffline|diff --git a/file2 b/file2]
+  1 hunks, 1 lines changed
+  [ ui.prompt|examine changes to 'file2'?
+  (enter ? for help) [Ynesfdaq?]] [ ui.promptecho|a]
+  
+  EDITOR: HG: Splitting 6432c65c3078. So far it has been split into:
+  EDITOR: HG: - [rev|2] split2, modifying file2
+  EDITOR: HG: Write commit message for the next split changeset.
+  EDITOR: split1, modifying file1
+  EDITOR: 
+  EDITOR: 
+  EDITOR: HG: Enter commit message.  Lines beginning with 'HG:' are removed.
+  EDITOR: HG: Leave message empty to abort commit.
+  EDITOR: HG: --
+  EDITOR: HG: user: test
+  EDITOR: HG: branch 'default'
+  EDITOR: HG: changed file2
+  [ ui.warning|transaction abort!]
+  [ ui.warning|rollback completed]
+  [ ui.error|abort: empty commit message]
+  [10]