Promote CompositeSVG to stable

Bug: 1101002
Change-Id: Iaa8538423acb119501092e098a7800ba690c0b89
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2399822Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805436}

third_party/blink/renderer/platform/runtime_enabled_features.json5

@@ -337,7 +337,7 @@
     },
     {
       name: "CompositeSVG",
-      status: "experimental"
+      status: "stable"
     },
     {
       name: "CompositingOptimizations",