Reland "[pdf] Use DW when it is an integer"

This is a reland of commit 712da0f86b0a8924bfee7f08c80ea321ef064634
This adds SK_IGNORE_PDF_DW_FIX to keep the old behavior until users can
be updated.

Original change's description:
> [pdf] Use DW when it is an integer
>
> This is a follow up to a previous change in which DW (Default Width) use
> was disabled [0]. For some reason, the PDF standard declared DW an
> integer even though advances are numbers (integer or real) everywhere
> else. Unfortunately, libpoppler appears to enforce this restriction and
> will use the default value of 1000 if DW is not an integer (like if it
> is a real). As a result, use of DW in Skia generated PDFs was disabled
> to avoid issues.
>
> This change restores the use of DW by only considering integer advances
> as candidates.
>
> [0] https://skia.googlesource.com/skia/+/6be3ea7a7d72a6a76efcbedf67dbfde465b1a9d9
>
> Change-Id: I724bb83989b7f8b1a8340890814ce43d27fdc822
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/708394
> Reviewed-by: John Stiles <johnstiles@google.com>
> Commit-Queue: Ben Wagner <bungeman@google.com>

Change-Id: I6bdcc630dfc9435896231b1cda7b66edf59ae6ac
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/709880
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
3 files changed