Add support for previews

[izadiegizabal]

Thanks for the nice library! Sadly the previews seem to break once adding the RSBlurShadow (via ComposeLevitation):

android. renderscript. RSDriverException: Failed to create RS context.   
at android. renderscript. RenderScript. internalCreate(RenderScript. java:1428)   
at android. renderscript. RenderScript. create(RenderScript. java:1530)   
at android. renderscript. RenderScript. create(RenderScript. java:1487)   
at android. renderscript. RenderScript. create(RenderScript. java:1461)   
at android. renderscript. RenderScript. create(RenderScript. java:1448)   
at com. gigamole. composeshadowsplus. rsblur. RSBlurShadowKt$rsBlurShadow$1$bitmap$2$1.invoke(RSBlurShadow. kt:201)   
at com. gigamole. composeshadowsplus. rsblur. RSBlurShadowKt$rsBlurShadow$1$bitmap$2$1.invoke(RSBlurShadow. kt:124)   
at androidx. compose. runtime. snapshots. Snapshot$Companion. observe(Snapshot. kt:503)   
at androidx. compose. runtime. DerivedSnapshotState. currentRecord(DerivedState. kt:200)  
(...)

[GIGAMOLE]

Nice, I will do it later.