Add support for TextFields with same fieldName, ie. TextFieldGroups

[imjosh]

A use case for this feature is multi-page documents with fields that are duplicated on each page (e.g. name and date on medical forms). Resolves #3361

Also, upgrade "rollup-plugin-terser" from 6.1.0 to 7.0.2 for optional chaining support.

Let me know if you'd like me to submit a pull request that combines this one with #3813

Example:

var { TextFieldGroup } = jsPDF.AcroForm;

var doc = new jsPDF({
  format: "a6",
  orientation: "landscape",
  unit: "mm",
  floatPrecision: 2
});

var txtName = new TextFieldGroup();
txtName.fieldName = "Name";
doc.addField(txtName);

var txtDate = new TextFieldGroup();
txtDate.fieldName = "Date";
doc.addField(txtDate);

addHeader();
doc.addPage();
addHeader();

function addHeader() {
  let yPos = 9;
  let xPos = 5;
  let txtChild;

  doc.text("Name:", xPos, yPos);
  xPos += doc.getTextWidth("Name:") + 1;
  txtChild = txtName.createChild();
  txtChild.Rect = [xPos, yPos - 6, 60, 9];

  xPos += 70;

  doc.text("Date:", xPos, yPos);
  xPos += doc.getTextWidth("Date:") + 1;
  txtChild = txtDate.createChild();
  txtChild.Rect = [xPos, yPos - 6, 35, 9];

  yPos += 5;
  doc.line(0, yPos, doc.internal.pageSize.width, yPos);
}