[DUX-2341] Parse "Module not found" messages

[9999years]

This will help us keep the module set in sync more reliably

See:

ghciwatch/src/ghci/mod.rs

Lines 700 to 747 in a97ecd3

	// TODO: This could lead to the module set getting out of sync with the underlying GHCi
	// session.
	//
	// If there's a TOATOU bug here (e.g. we're attempting to add a module but the file no
	// longer exists), then we can get into a situation like this:
	//
	// ghci> :add src/DoesntExist.hs src/MyLib.hs
	// File src/DoesntExist.hs not found
	// [4 of 4] Compiling MyLib ( src/MyLib.hs, interpreted )
	// Ok, four modules loaded.
	//
	// ghci> :show targets
	// src/MyLib.hs
	// ...
	//
	// We've requested to load two modules, only one has been loaded, but GHCi has reported
	// that compilation was successful and hasn't added the failing module to the target set.
	// Note that if the file is found but compilation fails, the file _is_ added to the target
	// set:
	//
	// ghci> :add src/MyCoolLib.hs
	// [4 of 4] Compiling MyCoolLib ( src/MyCoolLib.hs, interpreted )
	//
	// src/MyCoolLib.hs:4:12: error:
	// • Couldn't match expected type ‘IO ()’ with actual type ‘()’
	// • In the expression: ()
	// In an equation for ‘someFunc’: someFunc = ()
	// |
	// 4 | someFunc = ()
	// | ^^
	// Failed, three modules loaded.
	//
	// ghci> :show targets
	// src/MyCoolLib.hs
	// ...
	//
	// I think this is OK, because the only reason we need to know which modules are loaded is
	// to avoid the "module defined in multiple files" bug [1], so the potential outcomes of
	// making this mistake are:
	//
	// 1. The next time the file is modified, we attempt to `:add` it instead of `:reload`ing
	// it. This is harmless, though it changes the order that `:show modules` prints output
	// in (maybe local binding order as well or something).
	// 2. The next time the file is modified, we attempt to `:add` it by path instead of by
	// module name, but this function is only used when the modules aren't already in the
	// target set, so we know the module doesn't need to be referred to by its module name.
	//
	// [1]: https://gitlab.haskell.org/ghc/ghc/-/issues/13254#note_525037

_{From SyncLinear.com | DUX-2341}