Attempt to build unified extension.ts for browser/node

[ratmice]

This is an attempt to fix #1230 without duplicating the extension.ts file and fiddling with the import statement.
I'm pretty ignorant of javascript but this seemed to work for building both the desktop and web versions.

[ratmice]

Minor thing, I'm not sure I agree with the feature-request label, it seems just a plain old bug.
Because this PR makes things work with both the Running the Sample in the Desktop and Running the Sample in the Web sections of README.md.

[ratmice]

Just two more things I should note,

1. Testing on vscode.dev:
   When testing this example on vscode.dev the lsp example needs an open workspace. The only way I know of to do that at least on my browser is to Open a remote repository. Maybe that should be added to the README.md?

2. Should we expand this PR to any other examples?
   It's certainly possible that other examples in the repo could have a similar treatment, but it seems best to wait for a review before expanding the PR to more examples.