Avoid escaping paths when editing credentials

[jonathanhefner]

Shellwords.escape escapes unquoted spaces with a backslash, but Windows does not treat backslash as an escape character. Escaping is also a problem when paths are expressed in shortened 8.3 format (e.g. C:\Users\RubyOn~1\AppData\Local\Temp\...) because a backslash will be erroneously added before the ~.

We can avoid the need to escape by using system(command_name, *args) instead of system(command_line), but we must still support ENV["EDITOR"] values that embed command line arguments, such as subl -w.

This commit changes to system(command_name, *args), but uses Shellwords.split to extract any embedded arguments from ENV["EDITOR"]. This requires that Windows users put quotes around the entire path of their editor if it contains spaces, such as:

SET EDITOR="C:\Program Files\Microsoft VS Code\Code.exe" -w

In other words, the following are not supported on Windows:

SET "EDITOR=C:\Program Files\Microsoft VS Code\Code.exe"
SET EDITOR=C:\Program Files\Microsoft VS Code\Code.exe
SET EDITOR=C:\"Program Files"\"Microsoft VS Code"\Code.exe -w
SET EDITOR=C:\Program^ Files\Microsoft^ VS^ Code\Code.exe -w
SET EDITOR=C:\Program` Files\Microsoft` VS` Code\Code.exe -w

Fixes #41617 (again).
Closes #44890.

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This is based on my suggestion in #42728 (comment), with a fix for the test I mentioned in #42728 (comment).

/cc @ariccio @joshleblanc Would it be possible for you to test this change locally, and verify that it solves your issue?

[joshleblanc]

This change works on my end, and is a better solution than mine.

FWIW, your assumption that the temp path was coming from the environment variables was correct. It's set with the 8.3 filename in both TMP and TMP.