Support Vite+ (`vp pm publish`) as a package manager for publishing

Currently, changesets does not support publishing via Vite+'s package manager wrapper (vp pm publish).

Context:

Vite+ manages its own copies of package managers (e.g. pnpm) based on the version each project specifies, and exposes them through the vp CLI. This means a project can have a pnpm-workspace.yaml present without pnpm itself being installed globally — only vp is available, and Vite+ resolves and runs the appropriate package manager under the hood.

As a result, changesets' package manager detection incorrectly assumes a globally installed pnpm (or other package manager) is available, when in this setup only vp is.

Request:

Add support for detecting/using Vite+'s package manager resolution so that publishing can go through vp pm publish (and equivalent vp commands) instead of requiring the underlying package manager to be installed globally.

Additional context:

Raised originally in #2097 (comment) bur this is a separate feature request that's out of scope for that PR.