init SkSTArray storage before passing to SkTArray
init SkSTArray storage before passing to SkTArray

Using private inheritance is similar to having a class member,
except it's initialized before the next base class, SkTArray.
This lets us pass it to SkTArray's constructors.

I think we can make related changes (updating the various SkAlignedFoo,
not using them here, or not using them anywhere) independently.

... storage constructors made explicit at suggestion of GCC's -Wextra.
... now with explicit static_cast<STORAGE*>(this)

Change-Id: I665cf840e111da68f039416c9649ce328cc308d6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/333146
Reviewed-by: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>

google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia