feat(plugins): open plugin API 1.2 (#1654)

API 1.1.0 shipped with 0.1.37 and wit/ matched the released snapshot, so additions start with a bump: the package in wit/ and the SDK's copy, ENGINE_VERSION and both API_VERSION constants move to 1.2, and the official plugins and fixtures are rebuilt against it. No interface changes; 1.0 and 1.1 components keep linking. The release that ships 1.2 copies wit/ over the released snapshot.

plugins/official/string-tools/dist/plugin.wasm.sources

@@ -1 +1 @@
-ac745c20866ed959252778116af068d7264187a53df64e2de090522b7ba5b722
+fa82a8596bd6505c769c0125ea26cef9af08535b36f650ddc4a353eb50866cea