Show value of element inside an array/list when hovering over the key during debugging

[mystiquewolf]

Use email_message["internalDate"] in the examples below.

This feature request is for:

• During debug on hover over email_message the whole array/list of elements is shown
• During debug on hover over ["internalDate"] the value of the element with key internalDate is shown

See also microsoft/vscode#130610

[brettcannon]

Moved to #16995