Use correct character width for hexwidget.

[karliss]

Detailed description

• Use exactly the same font as one used for painting text
• Character width isn't an integer. For longer 4-8byte words error accumulates and can be visible for some fonts and font sizes.

Test plan (required)

• Select 8 byte item size and as many columns as possible
• make sure end of word is aligned with offsets at the top
• repeat with few different fonts and font sizes
• Try selecting bytes and text to make sure switching to floating point dindn't break any of the places that require integer division.
  • bytes as pair mode
  • multibyte items

Closing issues

Closes #1585

[ITAYC0HEN]

Looks very good, thanks!

[xarkes]

Thank you!