Implement SAFE_HEAP using acorn, and use it on user JS

[kripken]

Previously we instrumented the compiled code, and also code in JS libraries
using {{{ makeGetValue }}} etc., but not arbitrary HEAP8 etc. usage in user
JS code. This fixed that by adding a safeHeap pass to the acorn optimizer.

This found a few issues in our JS code too, which have been fixed in
recent PRs already.

[sbc100]

Do we still need the JS library technique of using {{{ makeGetValue }}} or can that now be removed in favor of this?

[sbc100]

Time to split this one one-element-per-line, or at least multiple lines?

[kripken]

Do we still need the JS library technique of using {{{ makeGetValue }}} or can that now be removed in favor of this?

We can maybe remove it, yeah. There is some advantage to the makeGetValue notation, in that you don't need to write the >> 2 etc., which can be error prone. But I agree it's probably not worth it given the verbosity, overall it's less clear. If you agree I can look into it.

[sbc100]

Do we still need the JS library technique of using {{{ makeGetValue }}} or can that now be removed in favor of this?

We can maybe remove it, yeah. There is some advantage to the makeGetValue notation, in that you don't need to write the >> 2 etc., which can be error prone. But I agree it's probably not worth it given the verbosity, overall it's less clear. If you agree I can look into it.

I wasn't suggesting removing {{{ makeGetValue }}} just that it should not try do any SAFE_HEAP stuff.. then the SAFE_HEAP stuff is all in one place and will be consistent between user code and library code?

[kripken]

Oh, yes, it is redundant atm. Rather than remove it, though, I'd prefer to eventually remove {{{ makeGetValue }}} entirely.