Compute the transformOrigin correctly, for negative values, when rendering AnnotationElements (bug 1627030)

This changes the `transformOrigin` calculations in `AnnotationElement._createContainer` and `PopupAnnotationElement.render`, to ensure that e.g. the clickable area of annotations and/or popups are both positioned correctly.

The problem occurs for *negative* values, since they're not negated correctly because of how the `transformOrigin` strings were build; see issue 12406 for a more in-depth explanation. Previously, for negative values, the `transformOrigin` strings would thus be ignored since they're not valid.

test/pdfs/bug1627030.pdf.link

@@ -0,0 +1 @@
+https://bug1627030.bmoattachments.org/attachment.cgi?id=9137808

test/test_manifest.json

@@ -780,6 +780,16 @@
        "annotations": true,
        "about": "Annotation with (ridiculously) large border width."
     },
+    {  "id": "bug1627030",
+       "file": "pdfs/bug1627030.pdf",
+       "md5": "4cde6134daa80449c43defd02c1393e2",
+       "rounds": 1,
+       "link": true,
+       "firstPage": 3,
+       "lastPage": 3,
+       "type": "eq",
+       "annotations": true
+    },
     {  "id": "issue4934",
        "file": "pdfs/issue4934.pdf",
        "md5": "6099da44f677702ae65a648b51a2226d",