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.

wit/plugin.wit

@@ -7,7 +7,7 @@
 /// or processes beyond WASI's clocks and randomness; everything else goes
 /// through the imports below, gated by the capabilities granted in
 /// `plugin.toml` (a missing one returns `error::denied`).
-package openidea:plugin@1.1.0;
+package openidea:plugin@1.2.0;
 
 world plugin {
     import log;