BREAKING CHANGE: Avoid collisions between static class/namespace members

This commit changes the delimiter between namespaces and their members
from "." to "::" in internal names. The new delimiter certainly feels
very un-JavaScript-y, but the meaning is still recognizable, and these
names aren't exposed to users in most cases anyway. Still, this is a
breaking change, as it affects the import names for `declare namespace`
members (as seen in tests/compiler/declare.js), and transform authors
will also need to update their code accordingly.

Fixes AssemblyScript#2793.

Author: CountBleck

lib/loader/index.js

@@ -371,7 +371,7 @@ export function demangle(exports, extendedExports = {}) {
     : exports["__setArgumentsLength"] || exports["__setargc"] || (() => { /* nop */ });
   for (let internalName of Object.keys(exports)) {
     const elem = exports[internalName];
-    let parts = internalName.split(".");
+    let parts = internalName.split(/\.|::/g);
     let curr = extendedExports;
     while (parts.length > 1) {
       let part = parts.shift();