Add POI API

[boholder]

By @Molitvan from Discord Not sure how likely it is for anyone to actually implement this, but it would be really cool to have an api for use in maps. I imagine it being based on commands and tags.

It would expose stuff like controlling the screen reader i.e. speaking, pausing, canceling... and also have a feature with which you could put a custom tag on a block or entity to make it be recognized as a point of interest. These tags would be something like poi-friendly (Marks an entity as friendly and enables sound cues and lockon for it. Friendly entities by default are stuff like animals.), poi-hostile (Marks and entity as hostile and enables sound cues and lockon for it. By default, hostile entities are mobs or anything that attacks you.), poi-interactable (Marks the block as interactable. By default the mod recognizes stuff like crafting tables, furnaces and chests as interactable.), poi-ore (This one is self explanatory. It marks a block as an ore.).

Maybe it could also make it possible to add navigation assist with you being able to create waypoints and paths and the mod could then guide you through them.

I am asking for this mainly because I've got a few ideas for maps and want to make them accessible and also because most existing maps are really hard to navigate if you have little to no vision or no vision at all.

Related to #148