[pathkit] Increase default memory size and allow growth Change-Id: Ib403708a8cbdcb85512c341c093d1c1fe342d2b3 Bug: skia:8216 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/502778 Reviewed-by: Nathaniel Nifong <nifong@google.com>