Add missing `is_query` function

[mmatyas]

While most of the Query-related functions are there, is_query was missing.

References:

• https://www.khronos.org/registry/OpenGL-Refpages/gl4/html/glIsQuery.xhtml
• https://www.khronos.org/registry/OpenGL/specs/es/3.0/es_spec_3.0.pdf#nameddest=section-6.1.7

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This change is 

[jdm]

Given servo/servo#24176, please make these changes in https://github.com/servo/sparkle instead.