Feature: Add size formatter

The `size` formatter returns the length of an array or string, or the
number of keys in an object.

Some APIs do not return a summary of their contents but only the full
list of contents. The `size` formatter can be used to still show such
count on a widget.

docs/widgets/services/customapi.md

@@ -54,12 +54,17 @@ widget:
             time: other key
         color: theme # optional - defaults to "". Allowed values: `["theme", "adaptive", "black", "white"]`.
         format: date # optional
+    - field: key
+      label: Number of things in array
+      format: size
 ```
 
-Supported formats for the values are `text`, `number`, `float`, `percent`, `bytes`, `bitrate`, `date` and `relativeDate`.
+Supported formats for the values are `text`, `number`, `float`, `percent`, `bytes`, `bitrate`, `size`, `date` and `relativeDate`.
 
 The `dateStyle` and `timeStyle` options of the `date` format are passed directly to [Intl.DateTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DateTimeFormat/DateTimeFormat) and the `style` and `numeric` options of `relativeDate` are passed to [Intl.RelativeTimeFormat](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat).
 
+The `size` format will return the length of the array or string, or the number of keys in an object. This is then formatted as `number`.
+
 ## Example
 
 For the following JSON object from the API:
@@ -100,6 +105,9 @@ mappings:
       locations:
         1: name # Citadel of Ricks
     label: Location
+  - field: locations
+    label: Location count
+    format: size # 2
 ```
 
 ## Data Transformation

src/widgets/customapi/component.jsx

@@ -4,6 +4,16 @@ import Container from "components/services/widget/container";
 import Block from "components/services/widget/block";
 import useWidgetAPI from "utils/proxy/use-widget-api";
 
+function getLength(data) {
+  if ('length' in data) {
+    return data.length;
+  } else if (typeof data === 'object' && data !== null) {
+    return Object.keys(data).length;
+  } else {
+    return NaN;
+  }
+}
+
 function getValue(field, data) {
   let value = data;
   let lastField = field;
@@ -85,6 +95,10 @@ function formatValue(t, mapping, rawValue) {
         numeric: mapping?.numeric,
       });
       break;
+    case "size":
+      value = getLength(value);
+      value = t("common.number", { value });
+      break;
     case "text":
     default:
     // nothing