Fix document selector warning in the extension

[kimadeline]

🦶 Repro steps

I couldn't repro it when running unit tests like mentioned in #1936, but it seems to appear in the dev tools (can be seen in the dev tools output copied by users in https://github.com/microsoft/vscode-python/issues/8661, #8636 and https://github.com/microsoft/vscode-python/issues/8567). I couldn't get it to appear in my dev tools output, but we should still fix the document selector schemes.

🔎 Impacted methods

• registerCodeLensProvider
• registerCompletionItemProvider
• registerDefinitionProvider
• registerDocumentFormattingEditProvider
• registerDocumentRangeFormattingEditProvider
• registerDocumentSymbolProvider
• registerHoverProvider
• registerOnTypeFormattingEditProvider
• registerReferenceProvider
• registerRenameProvider
• registerSignatureHelpProvider

🩹 Prescribed solution

We already have a predefined python document selector: the PYTHON constant from constants.ts, let's use it.

🛠 Todo

• jedi.ts: make sure that registerOnTypeFormattingEditProvider uses this.documentSelector too
• analysisOptions.ts: replace the const documentSelector assignment with const documentSelector = PYTHON (PYTHON from constants.ts) in getDocumentSelector
• intellisenseProvider.ts: replace the basic 'python' filter with PYTHON from constants.ts in L.58-60
• completionProvider.ts: update the activate method in LaunchJsonCompletionProvider (add scheme: 'file' to the first argument of registerCompletionItemProvider)
• completionProvider.unit.test.ts: update the deepEqual() calls
• datascience.ts: update registerCodeLensProvider
• make sure that none of the tests are failing

[karrtikr]

The warning is no longer visible in the logs, closing as stale.