DefaultShellCommandOption has an unreasonably small size limit

[samhocevar]

Summary of the new feature / enhancement

The DefaultShellCommandOption registry key has a size limit of 15 characters. This seems unreasonably small especially since DefaultShellArguments has a much larger limit and its contents are not used for a non-interactive shell, so a lot of what is in there has to be duplicated.

For instance, if I wanted to configure OpenSSH to use MSYS2 without creating a helper script, this is what my registry keys would look like:

DefaultShell                 C:\msys64\msys2_shell.cmd
DefaultShellArguments        -defterm -mingw64 -no-start -shell zsh
DefaultShellCommandOption    -defterm -mingw64 -no-start -shell zsh -c
DefaultShellEscapeArguments  0

Proposed technical implementation details (optional)

This PR increases the limit to the same value as DefaultShellArguments, which is currently PATH_MAX / 2 - 1.

[tgauth]

closing - available in 9.4 release