Fix symbol names used for outputting schedules into valid C++ source variable names

[derek-inteon]

Since Funcs and other classes can have user defined names, the resulting strings may be invalid C++ when used directly for variable names and identifiers during the source code generation for schedules.

This PR adds a 'conform_name' around all variable names being outputted to replace invalid characters with an underscore, to make sure only valid C++ identifiers are outputted for the schedule source.

[steven-johnson]

This function doesn't have anything to do with logging, and thus doesn't belong in ASLog.h

[derek-inteon]

Yes, that's true. I placed it here since it was a common header, and deals with formatting text, but it's not actually doing any logging.

Would you propose a new header/source file or some other location?

[dsharletg]

It looks like it's only used in the one source file LoopNest.cpp? I would just put it in there (in an anonymous namespace too).

[steven-johnson]

SGTM

[steven-johnson]

Where does this PR stand?

[steven-johnson]

Monday Morning Review ping: Where does this PR stand?

[steven-johnson]

Is this PR still active? If not, it will be closed.

[steven-johnson]

Is this PR still active?

[mcourteaux]

As this fix is rather ad-hoc, I think a more central place that legalizes all Func, Var and RVar names would be more reasonable, as that solves this issue for all auto-schedulers.

Also, there is already some sanitation happening here:

Halide/src/autoschedulers/adams2019/State.cpp

Lines 677 to 685 in 8bf7827

	// Sanitize the names of things to make them legal source code.
	schedule_source = src.str();
	bool in_quotes = false;
	for (auto &c : schedule_source) {
	in_quotes ^= (c == '"');
	if (!in_quotes && c == '$') {
	c = '_';
	}
	}

So this PR definitely needs changing.