Minor changes to texture definition RegExp, & added "FANCY" material enum (#290)

* Implement some missing `ui/` schemas

- Add `allow_debug_missing_texture`
- Add `propagate_alpha`
- Add `use_child_anchors`

* Tweak descriptions of `item_ref`

It should be noted that UI are referred to as "elements."

Moreover, the examples used colon (`:`) instead of dots (`.`) which contradicts the given description.

* Add more enum values to the `easing` property

These are all known values, aside from the five that was given.

* Update damage_source.json

The list of damage sources have been updated and added new possible damage sources.

Damage source `attack` has been deprecated going forward and has been split into two, namely: `entity_attack` and `entity_explosion`.

Damage source `fatal` has also been deprecated in newer format/`min_engine` versions, and has caused content log errors upon testing. But will remain for backwards compatibility.

This commit aims to resolve #185. Please refer to the damage sensor documentation here: https://github.com/MicrosoftDocs/minecraft-creator/blob/main/creator/Reference/Content/EntityReference/Examples/EntityComponents/minecraftComponent_damage_sensor.md

* Define `pack_scope` and `product_type` fields for pack manifests

With the release of Add-Ons in the marketplace, these property fields have become present in pack manifests.

* Tweak RegExp for defining texture names

- It will now match for a colon text (`:`) whereby namespaces are defined with
- Fix completely off-the-mark RegExp for `item_texture.json` and `terrain_texture.json` files.

* Add `FANCY` material enum

* Merge branch

source/resource/textures/flipbook_textures.json

@@ -20,7 +20,7 @@
       "atlas_tile": {
         "description": "UNDOCUMENTED.",
         "$comment": "UNDOCUMENTED",
-        "pattern": "^[a-z0-9_\\-]*$",
+        "pattern": "^[a-z0-9_:\\-]*$",
         "title": "Atlas Index",
         "type": "string"
       },