Remove outdated IDE server name in favor of language client

[koesie10]

This renames the ide-server.ts file to language-client.ts and renames all instances of IDE server to language client, which is the same name that VS Code uses. The only exceptions to this are when we are referring to the language server process itself, in which case I've renamed them to language server.

Checklist

• CHANGELOG.md has been updated to incorporate all user visible changes made by this pull request.
• Issues have been created for any UI or other user-facing changes made by this pull request.
• [Maintainers only] If this pull request makes user-facing changes that require documentation changes, open a corresponding docs pull request in the github/codeql repo and add the ready-for-doc-review label there.

[charisk]

Thanks!