Add deprecation notice for `@sentry/tanstackstart`

[nicohrubec]

This was meant as a utility package for shared logic between the solid and react variants of tanstackstart. It is unlikely that we will ever support the solid variant because of low usage and today this package is still empty and not used by anything so we should remove it.

[linear-code]

JS-2710

[github-actions]

A PR closing this issue has just been released 🚀

This issue was referenced by PR #22284, which was included in the 10.66.0 release.