The "Paths Separately" button in the simplify LPE should be a checkbox

Summary:

When clicking on the "Paths Separately" button in the Simplify LPE, it seems to work like a checkbox or a toggle button, so it would benefit from looking like one, instead of replacing the text within.

Steps to reproduce:

• open Inkscape
• draw a path
• open the path effects dialog
• select Simplify from the dropdown
• click on the "Paths Separately" button and observe

What happened?

The button works like a checkbox, but is a button.

What should have happened?

The button should be a checkbox.

Sample attachments:

Version info

Inkscape 1.4-beta (04c631c537, 2024-05-08, custom)

                      Compile  (Run)
    GLib version:     2.80.0
    GTK version:      3.24.41 (3.24.41)
    glibmm version:   2.66.7
    gtkmm version:    3.24.9
    libxml2 version:  2.12.6
    libxslt version:  1.1.39
    Cairo version:    1.18.0 (1.18.0)
    Pango version:    1.52.2 (1.52.2)
    HarfBuzz version: 8.4.0 (8.4.0)

    OS version:       Slackware 15.0 x86_64 (post 15.0 -current)