[IMP] web, *: add utils to get dataURL (base64) from file/blob

* = partner_autocomplete, point_of_sale, web_editor,
website_forum, website_slides

This can be used for example to preview an image from a file input field.

It can also be used to send the base64 content of the input by RPC instead of
having to rely on form submit as POST with multipart/form-data.

Technically wrap FileReader.readAsDataURL in a Promise.

This will also be used in task-1930726

PR: #33508

Signed-off-by: Quentin Smetz (qsm) <qsm@odoo.com>

addons/web/static/src/js/fields/basic_fields.js

@@ -1465,13 +1465,10 @@ var AbstractFieldBinary = AbstractField.extend({
                     this.do_warn(_t("File upload"), _.str.sprintf(msg, utils.human_size(this.max_upload_size)));
                     return false;
                 }
-                var filereader = new FileReader();
-                filereader.readAsDataURL(file);
-                filereader.onloadend = function (upload) {
-                    var data = upload.target.result;
+                utils.getDataURLFromFile(file).then(function (data) {
                     data = data.split(',')[1];
                     self.on_file_uploaded(file.size, file.name, file.type, data);
-                };
+                });
             } else {
                 this.$('form.o_form_binary_form').submit();
             }