Replaced s2 contains point methods with go-geom

[sams96]

Leads to significantly higher performance.

goos: linux
goarch: amd64
BenchmarkMatchesFilterContainsPoint-8               3902            312904 ns/op
BenchmarkMatchesFilterContainsPoint_Before-8          31          35054224 ns/op
PASS
ok      command-line-arguments  2.636s

From my testing while working on a project of my own I found that while using s2 types is very fast, converting to them is very slow, so if you're converting each time it's much faster to just use the go-geom types directly. This PR just changes this for contains point queries.

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This change is 

[manishrjain]

Thanks for the PR!

Reviewed 2 of 2 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved