Remove references to skstd::optional in Skia.

In this CL, Skia has been updated to use std::optional throughout.
skstd::optional continues to exist as a synonym for std::optional so
that Flutter does not break. The typedef will be removed in a few days,
once Flutter rolls into google3 have landed.

Original change's description:
> Revert "Reland "Remove skstd::optional entirely.""
>
> This reverts commit d161e2f6ecc802d069a61de71a4e7d9bc6b419cd.
>
> Reason for revert: Need to wait for Flutter fix to roll into Google3.
>
> Original change's description:
> > Reland "Remove skstd::optional entirely."
> >
> > This reverts commit 98e51006b9c1c8747ab99d6e2a738f64f5fc4f3b.
> >
> > Flutter fix: https://github.com/flutter/engine/pull/31193
> >
> > Original change's description:
> > > Revert "Remove skstd::optional entirely."
> > >
> > > This reverts commit 17d0fc087ced7f1deeea92de6404ce48f8433698.
> > >
> > > Reason for revert: flutter still uses the skstd class
> > >
> > > Original change's description:
> > > > Remove skstd::optional entirely.
> > > >
> > > > Skia now uses C++17's std::optional.
> > > >
> > > > Change-Id: I387069589baaefadd25e25bcec3f4cc6ee6fd090
> > > > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/501477
> > > > Reviewed-by: Ben Wagner <bungeman@google.com>
> > > > Reviewed-by: Brian Osman <brianosman@google.com>
> > > > Commit-Queue: John Stiles <johnstiles@google.com>
> > > > Auto-Submit: John Stiles <johnstiles@google.com>
> > >
> > > Change-Id: I2c001588007640ac7b8c9f0760038b46c220a07e
> > > No-Presubmit: true
> > > No-Tree-Checks: true
> > > No-Try: true
> > > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502702
> > > Auto-Submit: John Stiles <johnstiles@google.com>
> > > Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> > > Reviewed-by: Brian Osman <brianosman@google.com>
> > > Commit-Queue: Brian Osman <brianosman@google.com>
> >
> > Change-Id: Ia0cd41eda845b02f518c501a23293d344756a4eb
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502703
> > Reviewed-by: Brian Osman <brianosman@google.com>
> > Auto-Submit: John Stiles <johnstiles@google.com>
> > Commit-Queue: John Stiles <johnstiles@google.com>
>
> Change-Id: I8f89412292ba5dfe955c3f44c403c3c232cdad2b
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/503336
> Auto-Submit: Brian Osman <brianosman@google.com>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>

Change-Id: I28ef3f543bf74de72645485698affb54921a50f0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/504176
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
53 files changed