remove point aliases

This removes the notion of keeping track of every different t value
that resolves to the same or a similar point. Other fixes make
this concept unnecessary, and removing it simplifies the code.

This removes an allocation, and speeds up paths with many
overlapping curves.

As a bonus, four fuzzer tests that failed before now succeed.

TBR=reed@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2275703003

Review-Url: https://codereview.chromium.org/2275703003
9 files changed