Add functions for indirect draws and compute dispatches.

Resolves #1879.

- Add an 'indirectdraw' boolean field to the graphics feature support table returned by love.graphics.getSupported. This is almost always supported when compute shaders are supported, except on a few older phones.

- Add an 'indirectarguments' boolean field to the settings table in love.graphics.newBuffer.

- Add love.graphics.dispatchIndirect(shader, argumentsbuffer [, argumentsindex = 1]).
    The compute dispatch's threadgroup width, height, and depth values are fetched from the buffer (as 3 uints) instead of coming from function parameters.

- Add love.graphics.drawIndirect(mesh, argumentsbuffer, argumentsindex, x, y, ....).
    Vertex or index count, instance count, and other related parameters for drawing the mesh are fetched from the buffer (as 4 or 5 uints depending on whether the mesh has an index buffer) instead of coming from function parameters. It's usually a good idea to keep parameters other than the instance count in sync with what the mesh should be using.

- Add love.graphics.drawFromShaderIndirect(drawmode, argumentsbuffer [, argumentsindex = 1] [, maintexture = nil]) and drawFromShaderIndirect(indexbuffer, argumentsbuffer [, argumentsindex] [, maintexture = nil]).
    Vertex or index count, instance count, and other related parameters are fetched from the buffer as 4 or 5 uints, as above.

For the dispatch indirect arguments buffer, it has to have 3 uint32 elements: { uint threadgroupsX, uint threadgroupsY, uint threadgroupsZ }.

For non-indexed draws, the arguments buffer has to have 4 uint32 elements: { uint vertexCount, uint instanceCount, uint baseVertex, uint baseInstance }. Note that baseInstance should always be set to 0 as many drivers don't support non-zero values.

For draws which use an index buffer, the arguments buffer has to have 5 uint32 elements: { uint indexCount, uint instanceCount, uint firstIndex, uint baseVertex, uint baseInstance }. As above, the baseInstance value should always be 0.

A buffer can be created to have an array of those structures, which can be used with the argumentsindex parameter of the Indirect dispatch/draw functions.

src/modules/graphics/vertex.h

@@ -61,6 +61,7 @@ enum BufferUsage
 	BUFFERUSAGE_TEXEL,
 	BUFFERUSAGE_UNIFORM,
 	BUFFERUSAGE_SHADER_STORAGE,
+	BUFFERUSAGE_INDIRECT_ARGUMENTS,
 	BUFFERUSAGE_MAX_ENUM
 };
 
@@ -71,6 +72,7 @@ enum BufferUsageFlags
 	BUFFERUSAGEFLAG_INDEX = 1 << BUFFERUSAGE_INDEX,
 	BUFFERUSAGEFLAG_TEXEL = 1 << BUFFERUSAGE_TEXEL,
 	BUFFERUSAGEFLAG_SHADER_STORAGE = 1 << BUFFERUSAGE_SHADER_STORAGE,
+	BUFFERUSAGEFLAG_INDIRECT_ARGUMENTS = 1 << BUFFERUSAGE_INDIRECT_ARGUMENTS,
 };
 
 enum IndexDataType