Clean up kernel creation code in `codegen.driver`. Fix and dry-test SYCL codegen.

!449 (merged) accidentally broke SYCL code generation since SYCL kernels do not receive a launch config, but their kernel object expected one since it was being modelled as a GPU kernel.

This MR fixes this, alongside a few other improvements:

• Target.SYCL is no longer a GPU target
• SyclPlatform no longer inherits from platforms.GenericGpu, but directly from platforms.Platform.
• Emit SYCL kernels using codegen.Kernel instead of codegen.GpuKernel
• Combine the various kernel creation utility functions in codegen.driver into a KernelFactory class for cleaner code
• Move creation of Lambdas from Lambda.from_expression to KernelFactory.create_lambda
• Add dry-dock tests for SYCL code generation that only test if the codegen driver runs successfully

Relates to #126

src/pystencils/backend/platforms/sycl.py

@@ -24,12 +24,13 @@ from ..extensions.cpp import CppMethodCall
 
 from ..kernelcreation import KernelCreationContext, AstFactory
 from ..constants import PsConstant
-from .generic_gpu import GenericGpu
 from ..exceptions import MaterializationError
 from ...types import PsCustomType, PsIeeeFloatType, constify, PsIntegerType
 
+from .platform import Platform
 
-class SyclPlatform(GenericGpu):
+
+class SyclPlatform(Platform):
 
     def __init__(
         self,