[Impeller] Fix 1d threadgroup dispatch size, Implement drawPoint geometry computation with compute, fallback to specialized CPU. (#42060)

Compute shader implementation of https://github.com/flutter/engine/pull/41803

I found this to be generally more straightforward, and we can revisit the vertex shader approach with GLES.

Benchmark is pending here: https://github.com/flutter/flutter/pull/126728

Note: rendering behavior is identical even though this is now a single draw call. This is becuase strokes have overdraw prevention enabled by default, while this new contents does not

![image](https://github.com/flutter/engine/assets/8975114/29d84e0d-7be6-426a-b5e3-5226c1953a47)
18 files changed
tree: 379985124f3f3b0708ef4a7f863af41f96a42aef
  1. .github/
  2. assets/
  3. benchmarking/
  4. build/
  5. ci/
  6. common/
  7. display_list/
  8. docs/
  9. examples/
  10. flow/
  11. flutter_frontend_server/
  12. flutter_vma/
  13. fml/
  14. impeller/
  15. lib/
  16. runtime/
  17. shell/
  18. sky/
  19. testing/
  20. third_party/
  21. tools/
  22. vulkan/
  23. wasm/
  24. web_sdk/
  25. .ci.yaml
  26. .clang-format
  27. .clang-tidy
  28. .gitattributes
  29. .gitignore
  30. .pylintrc
  31. .style.yapf
  32. analysis_options.yaml
  33. AUTHORS
  34. BUILD.gn
  35. CODEOWNERS
  36. CONTRIBUTING.md
  37. DEPS
  38. Doxyfile
  39. LICENSE
  40. README.md
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