[11.x] Add stringable output to ProcessResult

[nuernbergerA]

Hey

im pretty sure @aarondfrancis can tell you why this is cool.

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Unfortunately PendingResult isn't macroable but i think its a common thing to work with the output as a stringable.

Currently you need to write this

Str::of(Process::run('ls -l')->output())->match('/some regex/');

With this PR it would be

Process::run('ls -l')->stringable()->match('/some regex/');

alternative API

Process::run('ls -l')->output(stringable: true)->match('/some regex/');

Cheers
Adrian

[aarondfrancis]

No opinions on the implementation, but I do really want this feature! 😍

Also, damn @nuernbergerA you're so fast!