Improve the dev container configuration experience

[egamma]

We currently have > 60 dev container configurations that are presented in a quick pick in alphabetical order, which is not very helpful.

[egamma]

Implemented a simple recommender for the predefined configurations based on the meta data that is included in the container definitions from the files included in the workspace.

The meta data includes information about the supported platforms and supported languages:

• The recommender detects platforms based on configuration files e.g. package.json is used to detect Node.js, sln, project.json, csproj for .NET core.
• The recommender counts the language files included in the workspace.

The recommender then assigns a score to a configuration based on the files contained in the workspace:

• If a configuration is for 'Any' files and platforms, then the config receives a score of 5
• If a configuration supports a platform that is detected in the workspace, then the config receives a score of +20.
• If a configuration supports a language that is contained in the workspace, then the config receives a score of +10.
• If a configuration supports a platform, that is not detected in the workspace, then the config is penalized with -20. This is to avoid that a configuration like the one for 'Azure Functions' appears as too popular when the workspace is not about Azure Functions.

The configuration picker sorts the configuration by score and initially only shows configuration with a score > 0. The quick pick includes a 'Show All...' item that shows all the available configurations.

For a node workspace the quick pick shows the following:

The second page shows the general containers with the 'Show all' entry:

FYI @Chuxel , @chrmarti