fcl-process: Un-deprecate TProcess.CommandLine on Windows

Summary

TProcess.CommandLine is marked as deprecated. This is a good thing for the Unix-like systems (Linux, FreeBSD, macOS, etc.) but is not good for Windows. I propose that FPC instead only remove it on the Unix-like systems.

First, an overview of how process arguments are passed on different systems.

• On Unix-like systems the environment block contains an argv[] array, which corresponds nicely to TProcess.Executable and TProcess.Parameters.
• On Windows however, an executable is handed a command-line string containing its name and the parameters, corresponding to the state of TProcess.CommandLine. The executable itself needs to parse the string into an argument array. This is usually handled by the C/C++ runtime or whatever other language runtime is here, but parsing behavior varies wildly.

And it is the fact that parsing behavior varies wildly on Windows that makes TProcess.CommandLine indispensable.

• A lot of important Windows utilities define their own parsing, including cmd.exe, msiexec, and many more. Among these, you definitely do not want to mess up cmd.
• Because cmd does not expand wildcards, many third-party programs choose to expand wildcards themselves when it sees one in an unquoted argument.
• Some of these third-party programs define their own parsing that is also incompatible with MSVC's. See the two links from 2019 and 2020 in https://cygwin.com/pipermail/cygwin-patches/2021q2/011367.html.

(I suspect OS/2 is similar, as Windows's behavior was inherited from DOS.)

Recommendation

• Keep TProcess.CommandLine deprecated on the Unix-like systems. The current emulation of it via CommandToList causes true Unix shell commands to break anyways, as the PeaZip people and I have recently discovered.
• Retain TProcess.CommandLine on Windows.
• Make sure TProcess.Parameters works the same on Windows for typical C/C++ programs as it does for Linux. (#41329 (closed))
• Make sure TProcess.Parameters is quoted in a way understood by FPC's own runtime library (it is currently not).

Details about current FPC RTL command line parsing

I don't want to open up another issue for that, but it will need to change.

• On Windows setup_arguments calls ParseCommandLine which does the parsing using a similar (Delphi?) syntax to CommandToList.
• On Darwin and WASI (not sure about other Linux), setup_arguments either does nothing or just copies from argv.

As a result the situation of 41329 would also apply to two echo programs compiled with FPC. With TProcess.Parameters set to only have one member '"a"':

• On Windows it would also only receive a in the parsed arguments because the command-line would be xxx.exe "a".
• On Darwin and WASI it would receive "a" in the parsed arguments because it is the exact form given in argv.