checker: fix struct field init with generic anon fn (fix #18294)

[yuyi98]

This PR fix struct field init with generic anon fn (fix #18294).

• Has been fixed by checker: fix struct field init with generic fn variable (fix #20847) #20878.
• Add test.

pub struct Module {
}

pub struct Service {
	callback fn () = unsafe { nil }
}

pub fn (mut self Module) do_anything[T]() {
}

pub fn (mut self Module) register[T]() {
	_ := Service{
		callback: fn [mut self] [T]() {
			self.do_anything[T]()
		}
	}
}

struct Something {
}

struct SomethingDifferent {
}

fn main() {
	mut mod := Module{}
	mod.register[Something]()
	mod.register[SomethingDifferent]()
	assert true
}

PS D:\Test\v\tt1> v run .

[spytheman]

Excellent.