This patch introduces a NativeModuleLoader::CompileAndCall that
can run a JS script under `lib/` as a function called
with a null receiver and arguments specified from the C++ layer.
Since all our bootstrappers are wrapped in functions in the
source to avoid leaking variables into the global scope anyway,
this allows us to remove that extra indentation in the JS source code.

As a start we move the compilation and execution of per_context.js
to NativeModuleLoader::CompileAndCall(). This patch also changes the return
value of NativeModuleLoader::LookupAndCompile() to a MaybeLocal
since the caller has to take care of the result being empty
anyway.

This patch reverts the previous design of having the
NativeModuleLoader::Compile() method magically know about the
parameters of the function - until we have tooling
in-place to guess the parameter names in the source with some
annotation, it's more readable to allow the caller to specify
the parameters along with the arguments values.