Regular expression precompilation & unicode property escapes

[guybedford]

Without a build supporting internationalization we don't get support for regular expressions.

For Fastly we fix this with a precompile step to replace in the source text all regular expressions with precompiled replaced variants - https://github.com/fastly/js-compute-runtime/blob/main/src/precompile.js.

We should do something similar in StarlingMonkey itself to support both regular expression performance and unicode property escape precompilation.