Implement fill action

[Pablete1234]

Adds a <fill> action that will place blocks in a block-bounded region.

• region (required) as property (either attribute, or children). If there's multiple children, they're considered a union.
• material (required) as attribute. Can be a material pattern like wool:15.
• filter (optional) as attribute. Filter what blocks get affected. ⚠️ may impact performance for large fills.
• events="true" (optional) as attribute, defaults to false. ⚠️ May impact performance for large fills.
  • If set to true, events will be called for block placements & block removals, meaning they will be affected by filters and can affect other pgm features (eg: they can cause damage to a destroyable).

The fill action works on the match scope.

Simple example:

<actions>
  <fill id="fill-with-air" region="some-region" material="air"/>
</actions>

Actual example, fills-in the region with water when any player is inside, and sets air when no one remains:

<actions>
  <fill id="fill-air" region="watery-region" material="air"/>
  <fill id="fill-water" region="watery-region" material="water"/>
  
  <trigger filter="has-players" action="fill-water" scope="match"/>	
  <trigger filter="no-players" action="fill-air" scope="match"/>
</actions>

<filters>
  <not id="no-players">
    <players id="has-players" filter="watery-region"/>
  </not>
</filters>