Summary

Add support for 32-bit builds. Mostly fixing a few places we were incorrectly using usize instead the fixed 64-bit Value size.

• Heap size limits are conservative: defaults range is 16MB to 128MB, and new max is 256MB.
• Note that HeapVIsitor::visit_value needs to explicitly convert between pointers/values instead of transmuting ref
• New max size for strings and array buffers on 32-bit platforms. Also added some overflow guards in to_index and typed array constructors.

Tests

• New CI job which runs integration tests compiled for 32-bit linux (i686-unknown-linux-gnu)