Attribute in portlet session cannot be found from theme

Issue

Set an attribute in a portlet's session, like this:

@Override
public void render(
        RenderRequest renderRequest, RenderResponse renderResponse)
    throws IOException, PortletException {

    HttpServletRequest httpServletRequest = PortalUtil.getHttpServletRequest(renderRequest);
    HttpSession httpSession = httpServletRequest.getSession();
    httpSession.setAttribute("myAttributeKey", "myAttributeValue");
    
    super.render(renderRequest, renderResponse);
}

Try to recover the value "myAttributeValue" in a custom theme's portal_normal.ftl (or some other template), like this:
```
${(request.session.getAttribute("myAttributeKey"))!"null"}
```
The value cannot be found (so null is printed) when the theme is rendered in a page where the portlet is deployed.
Listing all attributes shows the attribute key with a long prefix:
```
equinox.http.${my-portlet-package-name}myAttributeKey
```

Environment

Liferay DXP 7.3, 7.4

Resolution

In most circumstances, the prefix equinox.http.${my-portlet-package-name} is seamlessly added and removed when setting and getting an attribute.

One way to have this behavior in this situation as well is to use the original servlet request in the portlet, like this:

HttpServletRequest httpServletRequest = PortalUtil.getHttpServletRequest(renderRequest);
HttpServletRequest originalServletRequest = PortalUtil.getOriginalServletRequest(httpServletRequest);
HttpSession httpSession = originalServletRequest.getSession();
httpSession.setAttribute("myAttributeKey", "myAttributeValue");