begin refactoring SkTDynamicHash and SkTMultiMap

The biggest mismatch between these and SkTHash{Map,Set,Table}
is the old ones provide Iter and ConstIter, the new ones foreach().

This CL,

   - adds foreach() methods to the old types,
   - replaces all uses of ConstIter with foreach(),
   - replaces most uses of Iter with foreach(),

I'm leaving one spot using Iter to walk the table and remove its
elements for its own CL... it'll be a little more complicated to get
that right.

From there it should be straightforward to turn SkTDynamicHash
into a thin wrapper over an SkTHashTable.

Bugs: skia:9703
Change-Id: Ia6ba87c35b89585c42b5b9f118f4cbf3abd04f0d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/277098
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
12 files changed