The .vsix file can be built from the source code of vscode-texinfo.
First, clone the source code repository:
git clone https://git.sv.gnu.org/git/vscode-texinfo.git cd vscode-texinfo
Then, install dependencies with Node Package Manager, and build the project:
npm ci npm run package
If the operation is successful, a texinfo-{VERSION}.vsix file will be
generated under the root directory of the source code repository.