runtime namespace load order is independent from ordering in ns macro :require form

The order that namespaces are loaded at runtime is independent of the order that the namespaces are {{require}}d in user code. This seems to affect all optimization levels. This means that developers can't rely on side-effectful code in a given namespace to be run before another namespace that depends on the side effect is loaded.

Reproduction steps:

Running the command

will compile the a namespace defined in a.cljs. That namespace requires—via the :require form of the ns macro—namespaces b through g in alphabetical order.

After compiling, observe the following:

• The goog.addDependency call for a.js in the output out/cljs_deps.js file includes its dependencies in an arbitrary order. For example, one run on my machine resulted in:

• The console output given by running the compiled code with node out/main.js indicates that the runtime load order is identical to the ordering reflected in out/cljs_deps.js

Analysis:

It looks like some work to ensure the ordering at compile time was done as part of [CLJS-1453](https://dev.clojure.org/jira/browse/CLJS-1453), but it seems that things can get out of order by the time cljs_deps.js is emitted.

It seems that the output in cljs_deps.js for a given ClojureScript file is ultimately determined by the output of cljs.compiler/emit-source. The code there removes duplicate deps in the same way that the 'ns parse method in cljs.analyzer did prior to CLJS-1453.

The attached patch resolves the issue for my narrow use case, but I believe the underlying functions are passing the `:uses` and `:requires` around as maps, so more work may be needed for a full solution.