Previously, only strings could be used as identifiers for Angular services. This commit adds support
for using any value as identifier for an Angular service (e.g. used with `.provider()`,
`.factory()`, `.service()`, `.value()`, `.constant()`, `.decorator()`).

Among other things, non-string identifiers enable:
- Private services (without relying on naming conventions).
- Collision avoidance (without relying on custom prefixes and namespacing).
- Better toolability (e.g. autocomplete support for service identifiers).
- Better compression (i.e. strings can't be minified, non-string values could).

Identifiers for directives and filters are still restricted to string values, since they need to be
referenced in HTML (text).

--
For services with string IDs, the corresponding provider ID is constructed by appending `Provider`
to the service ID. For services with non-string IDs, the corresponding provider has the exact same
ID (it is the context that determines if a service or a provider should be injected).

E.g.:
```js
var bar = {};

angular.
  module('myModule', []).

  provider('foo' /* string ID     */, {$get: function () { return 'FOO'; }}).
  provider( bar  /* non-string ID */, {$get: function () { return 'BAR'; }}).

  config(['fooProvider', function (fooProvider) {
    // `foo` provider injected (because we are in config block)
  }]).
  run(['foo', function (foo) {
    // `foo` service injected (because we are in run block)
  }]).

  config([bar, function (barProvider) {
    // `bar` provider injected (because we are in config block)
    // (even though we used the same identifier (`bar`) that we will use in the run block)
  }]).
  run([bar, function (bar) {
    // `bar` service injected (because we are in run block)
  }]);
```

--
This change is backwards compatible (afaict).

Fixes #10347