patch-id fixes and improvements

These patches add fixes and features to the "git patch-id" command, mostly discovered through our usage of patch-id in the revup project
(https://github.com/Skydio/revup). On top of that I've tried to make general cleanup changes where I can.

Summary:

1: Fixed a bug in the combination of --stable with binary files and header-only, and expanded the test to cover both binary and non-binary files.

2: Switch internal usage of patch-id in rebase / cherry-pick to use the stable variant to reduce the number of code paths and improve testing for bugs like above.

3: Fixed bugs with patch-id and binary diffs. Previously patch-id did not behave correctly for binary diffs regardless of whether "--binary" was given to "diff".

4: Fixed bugs with patch-id and mode changes. Previously mode changes were incorrectly excluded from the patch-id.

5: Add a new "--include-whitespace" mode to patch-id that prevents whitespace from being stripped during id calculation. Also add a config option for the same behavior.

6: Remove unused prefix from patch-id logic.

V1->V2: Fixed comment style V2->V3: The ---/+++ lines no longer get added to the patch-id of binary diffs. Also added patches 3-7 in the series. V3->V4:
Dropped patch7. Updated flag name to --verbatim. Updated commit message descriptions. V4->V5: Updated commit message for patch 6.

Jerry Zhang (6):
patch-id: fix stable patch id for binary / header-only
patch-id: use stable patch-id for rebases
builtin: patch-id: fix patch-id with binary diffs
patch-id: fix patch-id for mode changes
builtin: patch-id: add --verbatim as a command mode
builtin: patch-id: remove unused diff-tree prefix

 Documentation/git-patch-id.txt |  24 ++++---
 builtin/log.c                  |   2 +-
 builtin/patch-id.c             | 113 ++++++++++++++++++++++++---------
 diff.c                         |  75 +++++++++++-----------
 diff.h                         |   2 +-
 patch-ids.c                    |  10 +--
 patch-ids.h                    |   2 +-
 t/t3419-rebase-patch-id.sh     |  63 +++++++++++++++---
 t/t4204-patch-id.sh            |  95 +++++++++++++++++++++++++--
 9 files changed, 287 insertions(+), 99 deletions(-)

base-commit: 45c9f05c44b1cb6bd2d6cb95a22cf5e3d21d5b63
Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-1359%2Fjerry-skydio%2Fjerry%2Frevup%2Fmaster%2Fpatch_ids-v5
Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-1359/jerry-skydio/jerry/revup/master/patch_ids-v5
Pull-Request: https://github.com/gitgitgadget/git/pull/1359

Range-diff vs v4:

 1:  321757ef919 = 1:  321757ef919 patch-id: fix stable patch id for binary / header-only
 2:  ec4a2422d5b = 2:  ec4a2422d5b patch-id: use stable patch-id for rebases
 3:  81501355313 = 3:  81501355313 builtin: patch-id: fix patch-id with binary diffs
 4:  bb0b4add03c = 4:  bb0b4add03c patch-id: fix patch-id for mode changes
 5:  b160f2ae49f = 5:  b160f2ae49f builtin: patch-id: add --verbatim as a command mode
 6:  dcdfac7a153 ! 6:  eef2a32f008 builtin: patch-id: remove unused diff-tree prefix

@@ Metadata
## Commit message ##
builtin: patch-id: remove unused diff-tree prefix

- From a "git grep" of the repo, no command, including diff-tree itself,
- produces diff output with "diff-tree " prefixed in the header.
+ The last git version that had "diff-tree" in the header text
+ of "git diff-tree" output was v1.3.0 from 2006. The header text
+ was changed from "diff-tree" to "commit" in 91539833
+ ("Log message printout cleanups").

- Thus remove its handling in "patch-id".
+ Given how long ago this change was made, it is highly unlikely that
+ anyone is still feeding in outputs from that git version.
+
+ Remove the handling of the "diff-tree" prefix and document the
+ source of the other prefixes so that the overall functionality
+ is more clear.

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