Consider to expose get_active_script_or_module and ActiveRunnable

[dtugend]

I can't judge mysef if it's a good idea at this point in time or not, but maybe it's possible to consider to expose get_active_script_or_module on the Context class and the ActiveRunnable enum, since it's currently private to the crate:

boa/core/engine/src/context/mod.rs

Line 819 in b345775

pub(crate) fn get_active_script_or_module(&self) -> Option<ActiveRunnable> {

The reason for this is that I'd like to implement a module / script source "load" / exec function that uses the current script's or module's Referrer to be able load files relative to that.