Send Extension recommendation when user changes language mode

[sana-ajani]

From user studies with students, we noticed upon downloading VS Code, the first thing many of them did was create a new file from the welcome page. Because the first line of code becomes the "filename" on the tab, many of them didn't realize they had to save their file. Instead, many of them noticed the option in the status bar to change the language mode and set it to their preferred language, but were lost on what to do to run their code or install an extension. Could we trigger the corresponding language extension recommendations when a user changes their language mode?