refactor: move StdLibs into extensions

[avik-pal]

julia> @time_imports using KernelAbstractions
     10.1 ms  UnsafeAtomics
      6.6 ms  Atomix
      0.7 ms  StaticArraysCore
    169.4 ms  StaticArrays
      0.4 ms  Adapt
      0.2 ms  AdaptStaticArraysExt
      1.9 ms  CEnum
      0.2 ms  LazyArtifacts
               ┌ 1.5 ms LLVMExtra_jll.__init__() 
    100.0 ms  LLVMExtra_jll 97.66% compilation time
               ┌ 0.2 ms LLVM.__init__() 
     30.7 ms  LLVM
      2.8 ms  UnsafeAtomicsLLVM
     12.1 ms  KernelAbstractions
      0.2 ms  StaticArrays → StaticArraysStatisticsExt

Moves both LinearAlgebra and SparseArrays into extensions. Saves around 250ms in load times (see #506)

[vchuravy]

Ah shoot. Shouldn't have merged this. This breaks users prior to the introduction of package extensions.