The client extension is still in an early state. It is usable but many advanced features have not yet been implemented. The syntax highlighting is also incomplete.
The client extension has not yet had a stable release. You can build and install it locally if you would like to experiment with it in the meantime.
First ensure that you have the node toolchain installed, then proceed as follows:
git clone --recursive https://github.com/wasm-lsp/vscode-wasm
cd vscode-wasm
npm i -g vsce
npm i
vsce packageThis will produce a vscode-wasm-<version>.vsix file in the project root.
Next, open Code and show the command palette (CTRL+SHIFT+P or CMD+SHIFT+P) and type install, then select Extensions: Install from VSIX... from the list. Point the file selector to the previously generated vscode-wasm-<version>.vsix. Finally, hit the reload button when prompted.