Add option to quantize time to whole frames of framerate.

This ensures that only whole frames are displayed. Good for ensuring the frames you see in the editor are what is shown at runtime and for creating more stop-motion like effects efficiently.

![CleanShot 2023-07-13 at 15 36 21@2x](https://github.com/rive-app/rive/assets/454182/c796c493-c359-469e-b5f4-8dd37686e7b7)

Diffs=
8b49fcbc5 Add option to quantize time to whole frames of framerate. (#5578)

.rive_head

diff --git a/.rive_head b/.rive_head
index d43528c..c71aee7 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-b8e5473b972f0253180c8c24d9752b16d7e4a499
+8b49fcbc5bc24452a1b1790af014060bf9d97ba9

submodules/rive-cpp

diff --git a/submodules/rive-cpp b/submodules/rive-cpp
index e3cac8d..7bcb9f1 160000
--- a/submodules/rive-cpp
+++ b/submodules/rive-cpp
@@ -1 +1 @@
-Subproject commit e3cac8d59b694547cd91b72627fbe85300a78b85
+Subproject commit 7bcb9f1c7ce89e7b4ea45b9ffae31aa4c3c8f1b3