fix(indent): underline highlight at correct column when tabs indent

[iammimikri]

Description

• indent plugin can't correctly underline first line of indent if user indents with tabs instead of spaces
• reason
  • user setting not checked and beginning of highlight moved by shiftwidth
  • e.g.: if shiftwidth is 4 then one indent highlight begins at col 3, two indents highlight begins at col 6 etc.
• solution
  • check if user has vim.bo.expandtab set
  • if true divide and round down start column by shiftwidth

Related Issue(s)

#404