Add random function for gcode macros.

[ardenpm]

Adds a random(min,max) function for gcode macros. Fixes #4001

[bubnikv]

Merged, reworked with 7353d8c
The thread local storage variables for the random number generator
were replaced by an external context variable.
Thread local storage is a scarce resource.

[smirgol]

I might be wrong but to me it looks like the rng is not initialized with a random seed before rolling for a random number, thus always producing the same random numbers.

Like put this in the Start G-code:
G1 X{random(1.0,3.0)} Y10 F3000 ; test
It will always produce this:
G1 X1.27095 Y10 F3000 ; test

Where X should be random and not always 1.27095

[ardenpm]

I might be wrong but to me it looks like the rng is not initialized with a random seed before rolling for a random number, thus always producing the same random numbers.

What platform are you running on? It may well depend on the implementation being used on your device by std::random_device which is permitted to use a pseudo-random number generator if a non-deterministic source is not available (see here.)

[smirgol]

I'm on linux and a friend of mine is on windows. We both get the same number.
std::random_device is not called in the affected code as far as I can see. I can find a reference to it in the SLA and the tests code, but that's not affecting the ones like MK3S as far as I understand it.

[ardenpm]

Looks like that might be part of the change @bubnikv made to remove my thread local storage.

[smirgol]

Seems so. I see that in your initial code you've seeded the generator, but that code got removed. :)

[bubnikv]

It should be fixed for the G-code generator with 6820921
Not on the main branch yet (I want to save myself some branch switching / merging for such a tiny change), but eventually it will end up there).

[smirgol]

Nice, thank you very much!

[HB-Stratos]

I wanted to use this new feature in the file name, so when exporting the same model twice while testing settings I would not have to always overwrite the old gcode file in the same folder. However I get the error that the random number generator is not available in the filename processing context. I see no practical reason why that limitation should exist, so, can this be changed?