Fix stencil preset next_pass stencil flags

[apples]

The stencil outline and x-ray presets were incorrectly using read+write stencil flags in their next_pass material.

Since materials normally cannot have both read and write stencil flags, the write flag would immediately get unset if the flags were poked at all.

This PR changes the preset next_pass materials to read only, and ensures that existing materials with read+write flags are correctly loaded with only the read flag set.

Related: #107767

[akien-mga]

Thanks!