Salsa - no support to treat files without a suffix as .js files, they are always treated as .ts files

[egamma]

extracted and summarized from microsoft/vscode#3508

Applications generated with the express generator have a file www without suffix but with the shebang

#!/usr/bin/env node

Code detects the file as a JS file and passes it to the tsserver. However, the tsserver treats this file as a .ts file and this results in type errors in a JS file.

To reproduce:

• git clone https://github.com/Microsoft/vscode-samples.git
• open the folder node-express-javascript in code
• open the file bin/www

Notice that there are errors from TS reported in this file,

[zhengbli]

This may require a tsserver API change to support opening a file as a specified ScriptKind, which will solve a more general category of issues.

[zhengbli]

With #7954, opening a file as a specific script kind is now supported.