Add boolean / string parameter support

[kaixoo]

Implements #59

[kaixoo]

@rodlie I see that the issue about adding boolean support is more about using a checkbox in the UI instead of a number? (as per MaurycyLiebner#323)

[rodlie]

I see that the issue about adding boolean support is more about using a checkbox in the UI instead of a number?

Shader effects that want a boolean param should get a boolean param (we have boolean param, must be exposed to shader plugins like other params).

Example:

• https://github.com/friction2d/friction-shader-plugins/blob/main/src/crossstitch.gre
• https://github.com/friction2d/friction-shader-plugins/blob/main/src/crossstitch.frag

<Property name="invert" nameUI="Invert" type="int" min="0" max="1" ini="0" step ="1" glValue="true"/>

[rodlie]

enve doc: https://maurycyliebner.github.io/docs/shaderEffects