Cloud Parameters Sandcastle broken with WebGL2 context

[ebogo1]

Console error messages show:

[Cesium WebGL] Fragment shader compile log: ERROR: 0:5: '=' : global variable initializers must be constant expressions
ERROR: 0:6: '=' : global variable initializers must be constant expressions

[Cesium WebGL] Fragment shader translation failed.
An error occurred while rendering.  Rendering has stopped.
RuntimeError: Fragment shader failed to compile.  Compile log: ERROR: 0:5: '=' : global variable initializers must be constant expressions
ERROR: 0:6: '=' : global variable initializers must be constant expressions

Sandcastle example: link

Browser: Chrome 97

Operating System: macOS 11.6

[ggetz]

Fixed with #10894