fn arguments default to capturing

[mojodojodev]

Following up from this discord comment

For closures the default is that they're capturing, for someone learning the language this will surprise them with an error:

fn outer(f: fn() -> None):
    f()

fn call_it():
    fn inner():
        print("inner")

    outer(inner)

error: Expression [4]:12:10: invalid call to 'outer': argument #0 cannot be converted from 'fn() capturing -> None' to 'fn() -> None'
    outer(inner) 
    ~~~~~^~~~~~~

This is a really nice error but is there any way of matching the defaults when defining a fn with the defaults when defining a fn argument so this:

fn outer(f: fn()):
    f()

Would expand to:

fn outer(f: fn() capturing -> None):
    f()

This would change the defaults so if you're marking a closure as @noncapturing you need to put the same tag in the fn argument:

fn outer(f: fn() noncapturing -> None):
    f()

fn call_it():
    @noncapturing
    fn inner():
        print("inner")

    outer(inner)

If there is some important optimization for fn arguments defaulting to non-capturing, it would be good if defining a closure also defaults to @noncapturing and you have to opt in to @capturing, just so long as the fn and fn as an argument have the same defaults so users don't have to be introduced to the complexity straight away.