[path] Add fill type utils

Introduce a couple of const helpers to facilitate migrating from
(non const) setFillType and toggleInverseFillType:

  - makeFillType:

    p.setFillType(ft)  ->  p = p.makeFillType(ft)

  - makeToggleInverseFillType:

    p.toggleInverseFillType()  ->  p = p.makeToggleInverseFillType()

Change-Id: I4516b3794cb5f2d8cb08c3cfeae534a295ba9e1b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/991198
Commit-Queue: Florin Malita <fmalita@google.com>
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
3 files changed