Add spell configuration to ItemGrant advancement

[arbron]

The advancements for granting (#1400) and choosing items (#1401) should have the option to modify any spells added:

• Select preparation mode (regular, always prepared, pact magic, at will, innate)
• Change limited uses
• Specify spellcasting ability

These options should be part of these advancements, but the controls should only be visible if a spell is added to an Item Grant advancement or the "Spell" type is selected in an Item Choice advancement.

The interface would be similar to this mockup by @MaxPat931

The configuration for these advancement types would gain something like this:

{
  configuration: {
    spells: {
      ability: null,          // Don't change the spellcasting ability
      preparation: "innate",  // Set to innate spellcasting
      uses: {
        max: "1",
        per: "lr"             // One casting per long rest
      }
    }
  }
}