Fix range when copying empty selection (#182227)

This fixes the range extensions get when copying an empty selection. As part of this, I've also:

- Added tests for this change
- Made the paste parts of the api optional. This is useful when a test provider only wants to add data on copy

extensions/vscode-api-tests/package.json

@@ -10,6 +10,7 @@
     "customEditorMove",
     "diffCommand",
     "documentFiltersExclusive",
+    "documentPaste",
     "editorInsets",
     "extensionRuntime",
     "extensionsAny",