add support for line numbering in the viewcode extention

[12rambau]

add support for line numbering in the viewcode extention

Feature or Bugfix

Feature

Detail

• I added a viewcode_show_lineos variale (default to False) to control wether or not line number shoud be added to the viewcode pages.
• This change the highlighter behavior in collect_pages method.
• The highliter will create a table with all the line number in one coloum and all the code in a second one. As viewcode is customizeing the first and last line of each tag, I created an offset variable that search for the second column tag and simply add it to point to correct lines when modifying the content.
• The new variable is documented and a short test check for the existence of the table in the output file.
• I decided not to change the display of the line numbers.
• for testing I checked using an extra build if the items are still modified in the table the same way.

I have 1 questions:

• what's the use this line:

  sphinx/sphinx/ext/viewcode.py

  Line 256 in 93226ca

  lines[0:1] = [before + '<pre>', after]

  It's 14 years old and when I check the output of line I only see 1 <pre> tag meaning that this is not changing anything.

Relates

Fix #10589

[AA-Turner]

I believe everything in this PR was contained in the older #6319 -- if there are any additional tests or etc we should add, please re-open!

A

[12rambau]

Ah sorry to have created a duplication. I checked before starting coding but didn't find out