Make fields in 'RenderBatch' struct public

[Tangenten]

• The issue is specific to Raylib-cs and not raylib
• I checked there is no similar issue already reported
• My code has no errors or misuse of Raylib-cs

fields are private, so cant do much with this struct. RenderBatch seems useful as a high performance way to build up a drawcall. Something im trying to optimize right now.

https://github.com/ChrisDill/Raylib-cs/blob/master/Raylib-cs/types/RenderBatch.cs

[Chris Dill]

Thanks! RenderBatch needed review and has been updated to fix this issue.