Pass viewport size to shadow pass instead of using Vector2i(1,1)

[jsjtxietian]

Fixes #82782

Two things to improve:

1. the argument order, I put p_viewport_size to the last but it may better be inserted somewhere front
2. If 1 is ok and in general this commit is ok, I will port it to compatibility mode.

[clayjohn]

Two things to improve:

1. the argument order, I put p_viewport_size to the last but it may better be inserted somewhere front
2. If 1 is ok and in general this commit is ok, I will port it to compatibility and mobile mode.

Putting it last is fine. This commit looks fine, please make the same change to the compatibility renderer and then it should be ready to merge!

[clayjohn]

Looks good to me!

Let's not cherrypick this one as it will introduce a behaviour change if someone was erroneously relying on VIEWPORT_SIZE being (1,1) (for example to modify the shader when in a shadow pass)

[akien-mga]

Thanks!