fix: resolve editor when getting doc context

[abeatrix]

Fixes an error that occurred when attempting to get the current VS Code document context. The previous methods for retrieving the active editor, document, and document text do not work with the new chat panel because when an user focuses on the webview panel we run the vscode.window.activeTextEditor, it would always returns undefined, cause Cody unable to fetch local context.

This replaces the previous logic with new utility functions getActiveEditorFromVisibleEditors, getCurrentVSCodeDoc, and getCurrentVSCodeDocText that more robustly retrieve the current document context that is not the focused webview chat panel.

Test plan

• Select some code in your editor
• In the new chat panel UI, type /test to run the test command
• Before the fix, Cody will tell you it doesn't have any context and cant identify the testing framework

AFTER

Screen.Recording.2023-11-17.at.7.53.15.AM.mov

BEFORE

Screen.Recording.2023-11-17.at.7.54.19.AM.mov

[abeatrix]

@umpox can i get a quick review from you, please 🙇‍♀️