Clarify the difference between sdkPath and sdkPaths #3994

Is your feature request related to a problem? Please describe.

There are two ways to configure the Dart path in VS Code (and similarly for the Flutter path). The first way is dart.sdkPath which is a single path to the binary or to the folder containing the binary. The other way is the plural dart.sdkPaths which is a list of paths that can be used for switching.

The problem is (at least for me), I thought these two ways were identical. I could either provide one location or a list of locations. So I removed the singular one and used the plural one exclusively. That's when things started to break and I didn't understand why.

It turned out I was wrong. The singular setting was the only one used for locating the sdk, while the plural one was used for switching. So the plural isn't meant to replace the singular one.

Describe the solution you'd like
This distinction can be made clearer in the explanation/docs of each setting.

Describe alternatives you've considered
I looked at https://dartcode.org/docs/quickly-switching-between-sdk-versions/ but it still wasn't clear that sdkPaths wasn't used for locating/searching.

Additional context
Discussion in Discord started here: https://discord.com/channels/608014603317936148/958861835971461120/979391354733998090