Problem:
Normally, `:drop +41 foo.txt` will open foo.txt with the cursor on line
41. But if foo.txt is already open, it instead is a no-op, even if the
cursor is on a different line.

Steps to reproduce:

    nvim --clean foo.txt
    :drop +30 foo.txt

Solution:
Handle +cmd in ex_drop().

Most callers of feed() do not expect feed() to dedent.
Now use a literal space in tests where it looks better.

Problem:    Sourcing buffer lines is too complicated.
Solution:   Simplify the code. Make it possible to source Vim9 script lines.
            (Yegappan Lakshmanan, closes vim/vim#9974)

https://github.com/vim/vim/commit/85b43c6cb7d56919e245622f4e42db6d8bee4194

This commit changes the behavior of sourcing buffer lines to always have
a script ID, although sourcing the same buffer always produces the same
script ID.

vim-patch:9.1.0372: Calling CLEAR_FIELD() on the same struct twice

Problem:  Calling CLEAR_FIELD() on the same struct twice.
Solution: Remove the second CLEAR_FIELD().  Move the assignment of
          cookie.sourceing_lnum (zeertzjq).

closes: vim/vim#14627

https://github.com/vim/vim/commit/f68517c1671dfedcc1555da50bc0b3de6d2842f6

Co-authored-by: Yegappan Lakshmanan <yegappan@yahoo.com>

Problem:  Wrong script context for option set by function defined by
          nvim_exec2 in a Lua script.
Solution: Call nlua_set_sctx() after adding SOURCING_LNUM and always set
          sc_lnum for a Lua script.

This is a bug discovered when testing #28486. Not sure if this actually
happens in practice, but it's easy to fix and required for #28486.

Problem:
Test sometimes fails on bsd (cirrus ci):

    test/functional/ex_cmds/swapfile_preserve_recover_spec.lua:589: retry() attempts: 464
    test/functional/ex_cmds/swapfile_preserve_recover_spec.lua:590: Expected objects to be the same.
    Passed in:
    (table: 0x0d5f1aa44070) {
      [1] = ''
     *[2] = ''
      [3] = '[Process exited 1]' }
    Expected:
    (table: 0x0d5ea3eb8718) {
      [1] = ''
     *[2] = '[Process exited 1]'
      [3] = '' }
    stack traceback:
      test/testutil.lua:104: in function 'retry'
      test/functional/ex_cmds/swapfile_preserve_recover_spec.lua:589: in function <test/functional/ex_cmds/swapfile_preserve_recover_spec.lua:556>

Solution:
Filter out empty items to avoid irrelevant redraw-timing assumptions.

Problem:
Indenting text is a common task in plugins/scripts for
presentation/formatting, yet vim has no way of doing it (especially
"dedent", and especially non-buffer text).

Solution:
Introduce `vim.text.indent()`. It sets the *exact* indentation because
that's a more difficult (and thus more useful) task than merely
"increasing the current indent" (which is somewhat easy with a `gsub()`
one-liner).

Problem:  When setting an option, mapping etc. from Lua without -V1, the
          script ID is set to SID_LUA even if there already is a script
          ID assigned by :source.
Solution: Don't set script ID to SID_LUA if it is already a Lua script.
          Also add _editor.lua to ignorelist to make script context more
          useful when using vim.cmd().

Problem:  When calling an API from Vimscript to set an option, mapping,
          etc., :verbose shows that it's set from an API client.
Solution: Don't override current_sctx.sc_sid when calling an API from
          Vimscript. Also fix the inverse case where API channel id is
          not set when calling an API from RPC. Move channel id into
          sctx_T to make saving and restoring easier.

Related #8329