[FEATURE REQUEST] FromValue::from_value should return a Result

[ranfdev]

I want to add support for TryFrom in the ValueDelegate macro

Eg, I want to do this:

#[derive(ValueDelegate)]
#[value_delegate(try_from = u32)]
struct MyU16(u16);

Clearly, the conversion from a u32 to a u16 could fail.
FromValue::from_value should return an error, else I can't return the error from the call of TryFrom::try_from.

Currently FromValue has an associated Checker which checks the type in the glib type system and throws an error when the conversion is not possible. A Checker can't be made to handle TryFrom though, because that would require calling try_from inside FromValue::check and FromValue::from_value, which is a waste of resources.

Or maybe I just panic if TryFrom fails