feature(developers): the inspector pages show a lot more info

The install path is stripped from file locations. Events & Hooks show
priorities and more usable descriptions for handlers that aren’t global
functions. Views show priorities, extensions, overrides, and any plugin
hooks that may filter their output.

Users can jump directly to plugin hook or view inspections from the views,
simple cache, and widgets listings.

We also move describeCallable() to the inspector.

Fixes #4540