cgen: fix struct field init with optional fixed array (fix #23195)

[yuyi98]

This PR fix struct field init with optional fixed array (fix #23195, fix #23193).

• Fix struct field init with optional fixed array.
• Add test.

type Arr = [4]u8

struct Foo {
	bar int
	baz ?Arr
}

fn main() {
	f1 := Foo{
		bar: 1
		baz: Arr([u8(5), 4, 3, 2]!)
	}
	println(f1)
	assert f1.baz as Arr == [u8(5), 4, 3, 2]!

	f2 := Foo{
		bar: 1
		baz: ?Arr(none)
	}
	println(f2)
	assert f2.bar == 1
	assert f2.baz == none

	arr := Arr([u8(5), 4, 3, 2]!)
	f3 := Foo{
		bar: 1
		baz: arr
	}
	println(f3)
	assert f3.bar == 1
	assert f3.baz as Arr == [u8(5), 4, 3, 2]!
}

PS D:\Test\v\tt1> v run .
Foo{
    bar: 1
    baz: Option(    Arr([5, 4, 3, 2]))
}
Foo{
    bar: 1
    baz: Option(none)
}
Foo{
    bar: 1
    baz: Option(    Arr([5, 4, 3, 2]))
}

_{Huly®: V_0.6-21636}

[felipensp]

Excellent, @yuyi98! Thanks.