fix #5871: ui: resize disk: show current and new size

The resize dialogs of VMs and containers only ask for the size
increment, so users have to look up the current size of the disk in
the config to know which size the disk will have afterwards.

Load the config of the guest in the dialogs and show the current size
of the disk, and the size it will have with the entered increment,
which gets updated while typing. As the dialogs load the size
themselves, callers do not need to change.

The size of the config is in the 'disk-size' format, where the units
are binary, while Proxmox.Utils.parse_size_unit() takes 'G' as GB, so
add a small parser for it, like parse_size() of PVE::JSONSchema.

Signed-off-by: Michal Fox <me@dualfroz.com>

www/manager6/Utils.js

@@ -1148,6 +1148,16 @@ Ext.define('PVE.Utils', {
             return `${per.toFixed(1)}% of ${maxcpu} ${cpu_label}`;
         },
 
+        // parses a size in the 'disk-size' format of the API, like '32G', into bytes
+        parse_disk_size: function (value) {
+            let match = /^(\d+(?:\.\d+)?)(?:([KMGT])(?:iB)?)?$/.exec(value);
+            if (!match) {
+                return undefined;
+            }
+            let exponent = ['', 'K', 'M', 'G', 'T'].indexOf(match[2] ?? '');
+            return parseFloat(match[1]) * 1024 ** exponent;
+        },
+
         render_bandwidth: function (value) {
             if (!Ext.isNumeric(value)) {
                 return '';