Get wasm sizes back down.

Turns out ```Optimize('Size')``` results in -Os and we get quite a bit more savings with -Oz.

Diffs=
f3739347c Get wasm sizes back down. (#6927)

Co-authored-by: Luigi Rosso <luigi-rosso@users.noreply.github.com>

.rive_head

diff --git a/.rive_head b/.rive_head
index da4ec7b..cc1de3e 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-a0a40213f0ea3490168fd71ad622e04ce364689b
+f3739347cf81c6c35d445da3678f987626ce7df3

build/rive_build_config.lua

diff --git a/build/rive_build_config.lua b/build/rive_build_config.lua
index f9543e7..93de598 100644
--- a/build/rive_build_config.lua
+++ b/build/rive_build_config.lua
@@ -445,7 +445,7 @@
 
     filter('options:config=release')
     do
-        optimize('Size')
+        buildoptions({ '-Oz' })
     end
 
     filter({})