get_maintainer: add --keywords-in-file option

get_maintainer: add --keywords-in-file option

There were some recent attempts [1] [2] to make the K: field less noisy
and its behavior more obvious.  Ultimately, a shift in the default
behavior and an associated command line flag is the best choice.

Currently, K: will match keywords found in both patches and files.

Matching content from entire files is (while documented) not obvious
behavior and is usually not wanted by maintainers.

Now only patch content will be matched against unless --keywords-in-file
is also provided as an argument to get_maintainer.

Add the actual keyword matched to the role or rolestats as well.

For instance given the diff below that removes clang:

:   diff --git a/drivers/hid/bpf/entrypoints/README b/drivers/hid/bpf/entrypoints/README
:    index 147e0d41509f..f88eb19e8ef2 100644
:    --- a/drivers/hid/bpf/entrypoints/README
:    +++ b/drivers/hid/bpf/entrypoints/README
:    @@ -1,4 +1,4 @@
:     WARNING:
:     If you change "entrypoints.bpf.c" do "make -j" in this directory to rebuild "entrypoints.skel.h".
:    -Make sure to have clang 10 installed.
:    +Make sure to have 10 installed.
:     See Documentation/bpf/bpf_devel_QA.rst

The new role/rolestats output includes ":Keyword:\b(?i:clang|llvm)\b"

$ git diff drivers/hid/bpf/entrypoints/README | .scripts/get_maintainer.pl
Jiri Kosina <jikos@kernel.org> (maintainer:HID CORE LAYER,commit_signer:1/1=100%)
Benjamin Tissoires <benjamin.tissoires@redhat.com> (maintainer:HID CORE LAYER,commit_signer:1/1=100%,authored:1/1=100%,added_lines:4/4=100%)
Nathan Chancellor <nathan@kernel.org> (supporter:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b)
Nick Desaulniers <ndesaulniers@google.com> (supporter:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b)
Tom Rix <trix@redhat.com> (reviewer:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b)
Greg Kroah-Hartman <gregkh@linuxfoundation.org> (commit_signer:1/1=100%)
linux-input@vger.kernel.org (open list:HID CORE LAYER)
linux-kernel@vger.kernel.org (open list)
llvm@lists.linux.dev (open list:CLANG/LLVM BUILD SUPPORT:Keyword:\b(?i:clang|llvm)\b)

Link: https://lore.kernel.org/r/20231004-get_maintainer_change_k-v1-1-ac7ced18306a@google.com
Link: https://lore.kernel.org/all/20230928-get_maintainer_add_d-v2-0-8acb3f394571@google.com
Link: https://lore.kernel.org/all/3dca40b677dd2fef979a5a581a2db91df2c21801.camel@perches.com
Original-patch-by: Justin Stitt <justinstitt@google.com>
Link: https://lkml.kernel.org/r/01fe46f0c58aa8baf92156ae2bdccfb2bf0cb48e.camel@perches.com
Signed-off-by: Joe Perches <joe@perches.com>
Tested-by: Justin Stitt <justinstitt@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>