analysis: fix namespaced reference lookup

[benjamin-thomas]

Hello!

This is an attempt at fixing this problem:

2 problems were occurring when activating the namespace feature

• The generated namespace module's path would be searched by its "double name" (MyNamespace-MyNamespace)
• The references command (from rescript-editor-analysis.exe references) would try to find the namespaced module (MyModule1-MyNamespace) against the indexed "public paths" and so would fail.

This PR solves the problem by:

• not trying to find the module name via file URI resolution when we already have its name in the package module index.
• mapping the "internal paths" (MyModule1-MyNamespace) to their public path equivalent (MyNamespace.MyModule1)

It looks like this is a long standing issue. I found this old open issue on the vscode plugin repo.

[EDIT] the latest commit on master related to yojson (166253d) broke the namespace config parsing (from rescript.json) so I branched off the commit before that (otherwise the test would break; no value could be provided for the namespace key)