Mark `TextmateLanguageService~context` argument as optional

[zm-cttae]

⚡️️ Feature Request

• [x] I'm using the latest version of vscode-textmate-languageservice available.
• [x] I searched existing issues, open & closed. Yes, my feature request is new.

Is your feature request related to a problem?

Currently the main class TextmateLanguageService depends on the vscode.ExtensionContext extension instance.
This isn't necessary thanks to VS Code API's extensions namespace.
We would also be able to initialise the service anywhere in the extension.

The signature is:

export default class TextmateLanguageService {
    constructor(public readonly languageId: string, public readonly context?: vscode.ExtensionContext) {
        // ...
    }
}

Describe the solution you'd like

We can use vscode.extensions.all - a public registry of vscode.Extension[]..
That can take ownership of all the extension contribution interfaces, and create a new custom registry.

Describe alternatives you've considered

Refactoring the vscode.ExtensionContext mock from test util into source code but why keep it?

[zm-cttae]

changed due date to April 01, 2023

[zm-cttae]

changed due date to May 01, 2023

[zm-cttae]

Keeping the vscode.ExtensionContext mock in order to test backwards compat of API.

[zm-cttae]

✅ Work is Definition of Done :)