cask: include resolved artifact targets in JSON output

Add a `target` sibling field per artifact entry in `Cask#artifacts_list`
(and therefore in `brew info --json=v2 --cask <name>`) containing the
absolute install path for `Relocated` artifacts (apps, fonts, plugins,
binaries, completions, etc.). Skipped for artifact types without a
target (pkg, installer, preflight blocks, zap) and in `uninstall_only:`
mode.

This lets external tooling — MDM agents, security scanners, packagers —
enumerate where a cask lands on disk without re-implementing Homebrew's
path-resolution logic (`Config` defaults, `HOMEBREW_CASK_OPTS`
overrides, `~` expansion, the `target:` DSL kwarg, etc.).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>