Allow positive decimal width in calligraphy tool (not just integers)

Split out from inbox#896 (closed)
Reported by @grootonnozelding

Steps to reproduce:

• Open Inkscape
• Switch to Calligraphy tool
• Try to set width below 1 (or just try to be more precise)

What happened?

• Truncated to integer values

What should have happened?

• Allow more control over width (and perhaps other settings?)
• 1 or 2 decimal values should be sufficient?
• Note: by default, width is dependent on zoom, but can be changed via absolute units.
• Absolute unit say they are in px, but seem to be in user unit px.

I think the pen will need to be set to positive decimals for UX purpose. Any artist knows his sizes and the expected result of such a setting. The issue is the output material. In this case a screen, that is also the input setting.

Inkscape Version and Operating System:

• Inkscape Version: alpha1 & beta1
• Operating System: all 64bit
• Operating System version: win10, LinuxMint18

Confirmed by me in 1.1-dev (838ae0f2, 2020-07-14, custom) Linux Mint 19.1