-- (double dash) should be treated as "end of flags" | Allow launching Rizin without a <file>

[caribpa]

Is your feature request related to a problem? Please describe.
After discussing in #593, and concluding with #614, it occurred to me that there's no reason for forcing the user to specify something as <file> parameter when launching Rizin.

Moreover, currently the "open without file/plugin" behavior is achieved by passing -- as <file> parameter to Rizin.
According to the POSIX Utility Syntax - Guideline 10:

The first -- argument that is not an option-argument should be accepted as a delimiter indicating the end of options. Any following arguments should be treated as operands, even if they begin with the '-' character.

Meaning: rz -- -test, rz -d -- -test, etc shall treat -test as <file> instead of just parsing -- and ignoring -test.

Try it with any non-built-in POSIX utility:

$ touch -- -test
$ ls -- -test
# -test
$ echo hi | tee -- -test
# hi
$ cat -- -test
# hi

Describe the solution you'd like

• -- is used to signal "end of flags" to be consistent with the standard command line utilities syntax.
• The user shouldn't be forced to pass a <file> to Rizin

$ rz
# Starts Rizin like if the current -- (and not -, a.k.a malloc://512) was passed

$ rz --
# Starts Rizin exactly in the same way as described above

$ rz -test
# Starts Rizin in the same way as described above and attempts to parse the '-t' flag with 'est' as value

$ rz -- -test
# Starts Rizin and opens the -test file

$ rz -d -- -test
# Starts Rizin with the -test file in debug mode

Describe alternatives you've considered
💔
Honestly, one could always use ./ or full/relative path to work around this:

$ rz ./-test
# Starts Rizin and opens the -test file

But there's still no reason for not allowing launching Rizin without <file>.

Additional context
This limitation is also present in radare2.

[ret2libc]

It seems actually reasonable and that it makes sense!

[XVilka]

The files to change are:

• librz/main/rizin.c
• rest of librz/main/*.c if we want to have the same behaviour for all Rizin tools.