Allow value with formula in variable filter

[Pablete1234]

Adds alternative syntax to variable filter where it will check for a formula's value instead of a single variable:

  <variables>
    <with-team id="red_score" var="score" team="red"/>
    <with-team id="blue_score" var="score" team="blue"/>
  </variables>

  <filters>
    <!--  Match-scoped checks for if either of the team is over the other, or tied -->
    <variable id="tied" scope="match" value="red_score-blue_score">0</variable>
    <variable id="red-winning" scope="match" value="red_score-blue_score">(0,oo)</variable>
    <variable id="blue-winning" scope="match" value="blue_score-red_score">(0,oo)</variable>

    <!-- The following use a single variable as the whole formula,
           meaning they're equivalent to their var counterpart, but could be more complex -->

    <!-- Team-scoped check for if you've gotten any score. 
         Players/teams would work, match would always abstain -->
    <variable id="has-scored" scope="team" value="score">(0,oo)</variable>
    <variable id="has-scored" var="score">(0,oo)</variable>

    <!-- Match-scoped check, which will redirect to checking for a specific team -->
    <variable id="red-has-scored" team="red" scope="team" value="score">(0,oo)</variable>
    <variable id="red-has-scored" team="red" var="score">(0,oo)</variable>

    <variable id="blue-has-scored" team="blue" scope="team" value="score">(0,oo)</variable>
    <variable id="blue-has-scored" team="blue" var="score">(0,oo)</variable>

    <!-- Match-scoped check, which will redirect to checking for all teams -->
    <variable id="any-has-scored" any="true" scope="team" value="score">(0,oo)</variable>
    <variable id="any-has-scored" any="true" var="score">(0,oo)</variable>
  </filters>

Before this would require an action that stored the result of red_score-blue_score in a tmp variable, then filtering on that tmp, now it can be automatically done by the filter.
Note that this can be combined with the team="x" and any="true" modifiers just like the normal variable filter.

Attributes:

value Required, the formula to check
scope Required, the scope that the formula runs against

These are an alternative to the original var. You can use either value+scope or var+index (if needed), but not both.

This type of variable filter is NOT dynamic.