[Impeller] Unify scale param for path and path component computation.

[luckysmg]

After #39917 landed, we compute vertex using scale.
But

engine/impeller/entity/geometry.cc

Line 267 in a098c91

.CreatePolyline(scale);

and

engine/impeller/entity/geometry.cc

Line 225 in a098c91

.CreatePolyline(scale);

pass scale to PathComponent.CreatePolyline but PathComponent using tolerance for it. So this PR is unify params they use and get correct result.

For test CanDrawArc

Before:

After:

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• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See [testing the engine] for instructions on writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
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• All existing and new tests are passing.

[chinmaygarde]

I just noticed it today. Was delightful to know it was fixed before I did :)

[luckysmg]

^_^