Loading worker modules should check permissions

[bartlomieju]

It turns out that when creating worker using new Worker("./path/to/module", ...); API there is no permissions check for modules loaded. Workers are much like dynamic imports (await import(...)) so similarly proper permissions should be checked when loading worker modules.

The problem we're facing is that TS compiler doesn't check permissions when op_fetch_source_file is called - so effectively it is priviledged, which is related bug at #4383.

Another problem I thought of is that there's no permission hooks in SourceFileFetcher; it handles redirects "transparently", ie. returning source code after resolving all redirect - permissions should be checked before performing any IO.

This is a bug that needs to be fixed before 1.0.