Add `start_line` and `end_line` information in `linkcode`

[u1735067]

Subject: Add start_line and end_line information in linkcode

Feature or Bugfix

• Feature

Purpose

• Allow the linkcode extension to add a line anchor in the generated link

Detail

• Add 2 info keys for linkcode_resolve: start_line and end_line (None by default)
• Use the viewcode-find-source event first to find the lines informations (to be used with sphinx-autoapi for example)
  • If it failed, optionally (linkcode_line_try_import setting) use the same import method as in sphinx.ext.viewcode (sphinx.pycode.ModuleAnalyzer) to find the line informations (same warning)
• Documentation updated (not sure this is correct though)

Relates

• I think it might close https://github.com/sphinx-doc/sphinx/issues/1556