LSP URI converter generate invalid paths when workspace URI has a trailing `/`

[SquidDev]

When running an extension using the vscode-test-web tool, the default workspace is mounted under vscode-test-web://mount/. This trailing / causes issues with the LSP URI converter.

For example:

• The code-to-protocol maps vscode-test-web://mount/a/file.txt to file:///workspacea/file.txt (rather than file:///workspace/a/file.txt).
• The protocol-to-code converter maps file:///workspace/a/file.txt to vscode-test-web://mount//a/file.txt (this isn't as serious, though does mean the URL is no longer normalised).

[dbaeumer]

Need to investigate.