Currently VSCode extension will try share diff views / scratch files
with Carbon language server. This results in following error:
> Request textDocument/semanticTokens/full failed.
Message: in call to `textDocument/semanticTokens/full`, JSON parse
failed: clangd only supports 'file' URI scheme for workspace files at
(root).textDocument.uri
Code: -32602
The change here updates vscode extension to filter for
`file://*/**.carbon` URIs, this matches how clangd extension does it:
https://github.com/clangd/vscode-clangd/blob/893dd905c2a6a7844fe32592796ef593e6f3bca6/src/clangd-context.ts#L18
Also updates tsconfig.json to node16 module resolution, this is done
since [automatic dependabot
PR](https://github.com/carbon-language/carbon-lang/pull/7575) seems to
have broken the build.
```
src/extension.ts:28:8 - error TS2307: Cannot find module 'vscode-languageclient/node' or its corresponding type declarations.
There are types at '/usr/local/google/home/davidloftus/carbon-lang/utils/vscode/node_modules/vscode-languageclient/lib/node/main.d.ts', but this result could not be resolved under your current 'moduleResolution' setting. Consider updating to 'node16', 'nodenext', or 'bundler'.
28 } from 'vscode-languageclient/node';
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Found 1 error in src/extension.ts:28
```
[vscode-languageserver-node](https://github.com/microsoft/vscode-languageserver-node/blame/93d5fe6f443dd6c8fe37f422c271d618edd121af/README.md#L159)
recomends updating to node16.