Implement @bitSizeOf

[Vexu]

Closes #2177

[data-man]

test "@bitSizeOf vector" {
    var v: @Vector(4, u31) = undefined;
    expect(@bitSizeOf(@Vector(4, u8)) == 4 * 8);
    expect(@bitSizeOf(@TypeOf(v)) == 4 * 31);
    expect(@bitSizeOf(@TypeOf(v[0])) == 31);
}

Nice! :)