New animation events + OnScriptEvent outputs for ai_hint

[Blixibon]

This PR adds the following new animation events:

• AE_VSCRIPT_RUN — Runs the specified VScript code on the animating entity. Handled on both the server and the client.
• AE_VSCRIPT_RUN_FILE — Runs the specified VScript file on the animating entity. Handled on both the server and the client.
• AE_CL_STOP_PARTICLE_EFFECT — Stops the specified particle effect. Use instantly to instantly remove all associated particles. From Alien Swarm SDK.
• AE_CL_ADD_PARTICLE_EFFECT_CP — Adds the specified particle effect control point. From Alien Swarm SDK.

This PR also hooks the animation event normally used for scripted_sequence into hint nodes so that it can fire OnScriptEvent outputs on AI hints. This is especially useful for actbusies which may require the same kind of world interaction which scripted sequences are capable of, although this can be used for any hint type as long as the NPC playing the animation recognizes it as their current hint.

This also fixes a crash which occurs when AE_NPC_RESPONSE is handled on a non-NPC or a NPC without an expresser.

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PR Checklist

• My PR follows all guidelines in the CONTRIBUTING.md file
• My PR targets a develop branch OR targets another branch with a specific goal in mind

[1upD]

LGTM