fmt: Make default_max_depth configurable

[ominitay]

There is currently no way to override this when using std.fmt.fmt(), and derived functions (anything.print(), std.log, etc). This small change allows overriding the default value. In future, there should likely be a specifier in the fmt string. That is probably best to be discussed in #1358, or an offshoot issue.

Closes #2370

[squeek502]

Closes, or at least contributes towards #2370

EDIT: Also might be worth reading this closed PR: #5412

[ominitay]

Would like to see what @andrewrk thinks about this, considering the closed PR, and that there seems to have been no further discussion since.

[Vexu]

#1358 looks like it is mostly implemented already, maybe we should discuss how this could be integrated into the argument system in #2370 before adding what looks like a workaround.

[ominitay]

I don't feel that this is a workaround. The default should be configurable IMO, and should be able to be overridden on a case-by-case basis.

[ominitay]

Anyway, I'd like to hear Andrew's thoughts on this, considering he had some plan in mind.

[Vexu]

Needs to be updated to use std.options.

[ominitay]

Will get that done soon :)

[ominitay]

Haven't been programming for a while, so please give my changes a little scrutiny ;)