startup: stdin as text instead of commands

Treat stdin as text by default (so the "-" file is not needed):
    echo foo | nvim

It works with file args (implemented in next commit), too:
    echo foo | nvim file1.txt file2.txt

Why? Because:
- Execution of input is (1) almost always unintentional/confusing,
  and (2) potentially destructive.
- Avoids the need for time-delayed warning.  #7659
- The _common_ case is to open text in a buffer, not send commands.

Note:
- Not for Ex-mode (-es) because it is used by scripts.  But maybe `-Es`?
- Not for --headless, because stdio may be a protocol stream and may be
  used for any purpose by stdioopen().

To treat stdin as Normal-mode commands, use `-s -` instead:
    echo ifoo | nvim -s -
Other alternatives:
  - Replay a register. E.g. the following mostly works, except @q aborts
    on any "beep" (e.g. if the cursor can't move).
    nvim -c '%d q|norm @q' -
  - Future: Let `:%source` work with unsaved buffer contents?

closes #2087
closes #7659

0 files changed, 0 insertions, 0 deletions