MiraclePtr: Manually exclude renderer sandbags

As a follow-up to https://crrev.com/c/5271003, we also manually exclude
fields thought to hurt renderer performance (when Renderer BRP is made
live). This is to complement ongoing rewrites that ignore
`RAW_PTR_EXCLUSION` (just to stay out of the way of Renderer BRP
experiments).

Bug: 41496832
Change-Id: I84eec4539c57cd7cd8daabfdc8214fb53cf85f5a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5269706
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Commit-Queue: Kalvin Lee <kdlee@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1265060}