Compiler config parsing is currently done with new Function(...) which
is a XSS vulnerability. Replacing this with json parsing for safety
reasons.
Almost all compiler options (except for moduleTypeProvider) are json
compatible, so this isn't a big change to capabilities. Previously
created playground URLs with non-default configs may not be compatible
with this change, but we should be able to get the correct config
manually (by reading the JS version)
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