fix(lambda): Updates for Lambda quick edit

[rhamilt]

This PR contains updates for miscellaneous features related to the new Lambda quick edit.

Handling of empty directories

Problem

Previously, having an empty directory in the Lambda quick edit flow led to errors when trying to view the function code in the explorer or in a workspace. An empty folder could be the result of an error during download. The unintended bug in the code was related to how we were checking for existence of a function saved locally.

Solution

Check if there are any files in the directory before determining if it exists locally. If the directory is empty, we must redownload the code (a Lambda function cannot be empty, so we know it is unintended)

README updates

Problem

• A couple typographic errors
• README was opening as separate tab, not as split pane
• README was referencing "cloud deploy icon" rather than showing the actual icon, same with the invoke icon

Solution

• Fix errors
• Adjust README open to use markdown.showPreviewToSide
• Save the icons locally so we can display them in the actual README.

Quick Edit Flow updates

Problem

• Some non-passive metrics were being emitted on activation
• Downloading code on activation lead to race conditions with authentication
• Downloading code on activation lead to extra slow load times

Solution

All of this is fixed by moving things around so that there is never any code downloaded during activation. This is beneficial because it keeps us from doing a lot of our main functionality on activation.

Previously, opening a function in a workspace, which could be done through a URI handler or from the explorer, would cause the extension to restart. Once the extension restarted, at that point we would download the code and start the watchers. These changes download the code first, and only start the watchers on activation. Because the user doesn't need to be authenticated to start the watchers (only to deploy), this is not an issue for being authenticated. If it's a workspace folder, we're assuming the function exists locally, so that's why we know we've downloaded the code already.

The only edge case is if the local code is out of sync with what's in the cloud; in this case, we prompt the user to overwrite their code, but they need to go to the explorer to manually download it to avoid the activation race conditions.

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[roger-zhangg]

So this confirm deleted all data in folder but didn't download anything?

[rhamilt]

Yes, we want to clear the folder so that next time we try to open the code, editLambda knows it needs to redownload the freshest code.