TS Bindings: check if has NPM, throw useful error + instructions, and fix broken links to old soroban docs

[chadoh]

Reported by a user:

After running bindings typescript it returns an error, "program not found". And while it does generate some typescript files, the node modules folder as well as the dish folder is missing.

This happens because right now we assume that you have Node/NPM, rather than verifying and erroring with a more useful error message.

Let's check if Node & NPM are installed and, if not, error with this explanation:

This command generates an NPM package for use with a NodeJS codebase. You need Node/NPM to build the generated package, and you'll also need it to import and use it. There are many ways to install Node; a popular way is nvm, Node Version Manager: https://github.com/nvm-sh/nvm

[leighmcculloch]

Suggested tweaks to the explanation to remove the you's:

This command generates an NPM package for use with a NodeJS codebase. Node/NPM is required to build the generated package, import it, and use it. See https://nodejs.org/en/download to install Node/NPM.

The node website shows a variety of install options and by default shows the nvm instructions.

[janewang]

For cleaning up and add checks and errors, could we also clean up the old links to soroban-docs. We have merged all docs under stellar docs.

[janewang]

we are not going to use npm anymore, closing

[leighmcculloch]

This was closed in favor of:

• Change the default to not npm build #1512