Shiny Updates: Use plugin file rather than slug as identifier

[obenland]

After [36205] we're now able to use the plugin file as a unique identifier for plugins. The slug can be ambiguous, as downloading Hello Dolly from the plugin repository reveals pretty easily.

[obenland]

Two plugins, same slug, unique plugin file.

[adamsilverstein]

Looks great @obenland:

I tested this patch and shiny updates continue to operate as expected on both the plugin screen and the install screen.

I appreciate the way you are bringing over bug fixes from the shiny updates feature plugin back into core! As you so elegantly describe, slugs may not be unique and this causes issues with shiny updates: using the plugin file/path itself ensures uniqueness and fixes these cases.

[obenland]

In 36221:

Plugins: Use plugin file rather than slug as identifier

The plugin file is unique while there can be more than one plugin with the
same slug. This also allows us to simplify the way updates from the plugin
detail iframe are executed.

See [36205].
Fixes #35350.