support multiple perferred server roots (#476)

[lixvbnet]

This PR is to resolve #476

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To go beyond #155, it would be nice if we can set multiple preferred server roots as one string, just like how we set PATH variable.

• /path/to/root1:/path/to/root2:/path/to/root3
• /dist:/build:/output:/publish
• nice to support "." too, which stands for the folder where the open file is located

If none of the directories exists, it defaults to the workspace root.

[lixvbnet]

@microsoft-github-policy-service agree

[andreamah]

Thanks for looking into this! Thinking about it more, I would probably prefer a setting that can take an array or string (instead of just parsing the string from within the extension). For example, the npm.exclude setting that is built into VS Code has this:
https://github.com/microsoft/vscode/blob/93b691ea016f4ee8dc8d2edfde9f897fb733445e/extensions/npm/package.json#L255-L258
This way, it is more consistent with what we have in other extensions.

[lixvbnet]

Fair point. Just updated the commit.

[andreamah]

One more thing: could you update the setting to specify what the array value would describe (ie: precedence and first is highest)?

[lixvbnet]

Sure, will do. (Edit: Done. updated the commit.)

Just found another glitch while playing around with current branch. It sometimes doesn't work as expected, because the server seems to have caching that it doesn't always respect the root value returned from the utility function.

For example, with "serverRoot" set to ["/dist", "/publish"] and there's an "index.html" file inside each folder.

1. Preview dist/index.html
2. Preview publish/index.html

Step 2 will still be previewing the content of dist/index.html same with step 1, unless I stop the server and preview again.

Having similar issue with ".", as its resolved value is always changing while switching among different files.

Do you have any idea on this?
If there's no easy fix, or it's an expected behavior, then this PR has to be dropped, I think, to avoid bringing confusion.