[Bug]: library.getContents() sometimes returns an empty JSON array

[Azhrei]

Describe the Bug

Calling library.getContents() can often return an empty JSON array when there are multiple properties and macros on the Lib: token.

(See this Discord post.)

To Reproduce

1. Place this code into a macro inside a campaign with one or more Lib: tokens:

[r, foreach(vTokenLibrary, library.listTokenLibraries(), "<br>"), code: {
    [r: vNameSpace = json.get(vTokenLibrary, "namespace")]
    [library.getContents(vNameSpace)]
}]

2. When executed, the output will typically be one line per Lib: token with an empty set of brackets as the value. (Sometimes it may work. See below.)

Expected Behaviour

Each Lib: token that contains macros or properties should produce a non-empty list of those values.

Here is example output from a campaign with multiple Lib: tokens showing how the output should look. Note that the first Lib: token, Coords, has no macros and no properties.

  | Anonymous User: Coords []
  GlobalsSRDPF ["property/elevation","property/editonload","property/daylast","property/tokenuncimgchange","property/fgmsecret","property/maps","property/hpbar","property/startmap","property/monthlast","property/skillsindex","property/tempmodlist","property/deathpoints","property/tempmodtogglesets","property/yearlast","property/playersgm","property/system","property/mapstemplate","property/handouts","property/systems","property/skilltype","property/skillssys","property/deathpoint","property/hpbars"]
  CannedSpeech_v1 ["macro/displaySpeech","macro/Canned Speech Frame","macro/Launch Canned Speech","macro/Say Speech","macro/Edit Speech","macro/Manage Speech","macro/Edit Speech .alt","macro/Speech.css","macro/onCampaignLoad","macro/Manage displayPrefs","macro/json.psort","property/elevation","property/jaw_speech_display_prefs","property/jaw_display_prefs","property/prefs"]
  cifTemplates ["macro/TemplateInfo","macro/drawTemplate","macro/onCampaignLoad","macro/removeTemplate","macro/lastTemplateDrawn","macro/SetSourceMap","property/elevation","property/ac","property/constitution","property/strength","property/sourcemap","property/hp","property/description","property/charisma","property/intelligence","property/wisdom","property/dexterity","property/lasttemplatedrawn","property/defense","property/movement"]
  disguise ["macro/Disguise","macro/autoDisguiseButton","macro/Use Disguise","macro/onCampaignLoad","property/elevation","property/h.disguise","property/h.disguisemacro","property/ac","property/constitution","property/strength","property/hp","property/description","property/charisma","property/intelligence","property/wisdom","property/dexterity","property/defense","property/movement"]
  chat ["macro/output","macro/<b>Impersonate</b>","macro/getGMNames","macro/output.basic","macro/json.type","macro/getTokenInfo","macro/icc","macro/updateTargets","macro/onCampaignLoad","macro/jsonToVars","macro/validateTokenInfo","property/elevation","property/bot_doortimer","property/ac","property/rpe.options","property/constitution","property/rpe.macrogroups","property/strength","property/hp","property/description","property/rpe.allindexes","property/charisma","property/intelligence","property/wisdom","property/dexterity","property/defense","property/movement"]
  players ["macro/output","macro/<b>Debug Off</b>","macro/<b>Debug On</b>","macro/watch","macro/chat","macro/text","macro/label","macro/onCampaignLoad","macro/script","macro/pause","property/elevation","property/ac","property/rpe.options","property/constitution","property/rpe.macrogroups","property/strength","property/hp","property/description","property/rpe.allindexes","property/charisma","property/intelligence","property/wisdom","property/dexterity","property/defense","property/movement"]

Screenshots

In many cases, executing the above macro will produce output that looks like this:
| Anonymous User: Coords []
GlobalsSRDPF []
CannedSpeech_v1 []
cifTemplates []
disguise []
chat []
players []

### MapTool Info

_No response_

### Desktop

_No response_

### Additional Context

It appears that `listLibraryContents()` from `src/main/java/net/rptools/maptool/client/functions/LibraryFunctions.java` is creating a `CompletableFuture` but not waiting for it to finish, so the JSON object is returned and (potentially) used before being populated with data.