Add folding tests

[xpyctumo]

LS supports folding, but we don't have any tests on that

The basic keyboard shortcuts for interacting with this in VS Code are:

Fold folds the innermost uncollapsed region at the cursor:
Ctrl + Shift + [ on Windows and Linux
⌥ + ⌘ + [ on macOS
Unfold unfolds the collapsed region at the cursor:

Ctrl + Shift + ] on Windows and Linux
⌥ + ⌘ + ] on macOS
Fold All folds all regions in the editor:

Ctrl + K, Ctrl + 0 (zero) on Windows and Linux
⌘ + K, ⌘ +0 (zero) on macOS
Unfold All unfolds all regions in the editor:

Ctrl + K, Ctrl + J on Windows and Linux
⌘ + K, ⌘ + J on macOS

This will be needed to understand what type of request needs to be sent in the tests to work