can't edit Stop Offset of first and last stops in gradient toolbar.
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#### Summary:
- can't change/edit Stop Offset of first and last stops in gradient toolbar.
#### Steps to reproduce:
<!-- Describe what you did (step-by-step) so we can reproduce: -->
- open Inkscape
- create shapes and apply gradient.
- select gradient tool and select frist / last stop.
- you'll see you can't able to update/edit Stop Offset in the toolbar but you can edit them in new gradient editor.
#### What happened?
doesn't able to change/edit Stop Offset of first and last stops in gradient toolbar. (see attached video)
#### What should have happened?
should be able to change/edit Stop Offset of first and last stops in gradient toolbar.
#### Debug info
```
Inkscape 1.2-dev (3024607aaf, 2021-06-23)
GLib version: 2.68.3
GTK version: 3.24.29
glibmm version: 2.66.1
gtkmm version: 3.24.5
libxml2 version: 2.9.10
libxslt version: 1.1.34
Cairo version: 1.17.4
Pango version: 1.48.5
HarfBuzz version: 2.8.1
OS version: Arch Linux
```
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issue