TileMap's set_cell could use a little clarification

**Your Godot version:**
v. 4.0.2

**Issue description:**
Godot's tile system is very advanced, but the documentation could be improved in a few places. As an example, as someone who likes to build games which, at least partially, generate their own maps, I need to understand the usage of set_cell for TileMap.

According to the documentation, set_cell "sets the identifiers" for a cell. I am not 100% sure what that specifically means, I only have the gist of it. I believe that it basically means that it changes the tile assigned to a cell, but am not 100% certain that it doesn't go beyond that, even now.

It does this on a "layer", but does not specify if it's referring to the tile map itself, or the tile set that the map is using. Experimentation shows that it's the map, but this isn't adequately addressed. "Layer" is a commonly used term in many game engines and some explanation here would be very helpful.

source_id is identified as a "TileSet source ID", without explaining what that means to me here. I'm still a little foggy on it. It appears to mean what I used to call the tile set layer; but again, this isn't perfectly clear.

Mostly I feel that such a fundamental function could use a spiffier, and more applicable, documentation for people just getting started in terrain scripting; or people moving in from other engines. The system is very useful, but perhaps someone who knows the internal code better than I do could expand on the description of the properties and methods?

**URL to the documentation page (if already existing):**
https://docs.godotengine.org/en/stable/classes/class_tilemap.html#class-tilemap-method-use-tile-data-runtime-update