fix: allow multiline message for echoerr (neovim#25380)

PROBLEM:

Currently `:echoerr` prints multi-line strings in a single line
as `:echom` does (Note: `:echon` can print multi-line strings well).
This makes stacktrace printed via echoerr difficult to read.

Example code:

    try
      lua error("lua stacktrace")
    catch
      echoerr v:exception
    endtry

Output:

    Error detected while processing a.vim[5]..a.vim:
    line    4:
    Vim(lua):E5108: Error executing lua [string ":lua"]:1: lua stacktrace^@stack traceback:^@^I[C]: in function 'error'^@^I[string ":lua"]:1: in main chunk

SOLUTION:

Allow echoerr to print multiline messages (e.g., lua exceptions),
because this command is usually used to print stacktraces.

Output after the fix:

    Error detected while processing a.vim[5]..a.vim:
    line    4:
    Vim(lua):E5108: Error executing lua [string ":lua"]:1: lua stacktrace
    stack traceback:
            [C]: in function 'error'
            [string ":lua"]:1: in main chunk

NVIM v0.9.4

NVIM v0.9.3

NVIM 0.9.4

This is a maintenance release, focusing on bugfixes.

BUG FIXES
- build: Fix exporting symbols on macOS Sonoma
- api: Handle NUL in nvim_err_write() and nvim_out_write()
- autocmd: Api functions accepting garbage after event name
- clang: Null pointer dereference in parse_msgpack
- clipboard: Don't pass --foreground to wl-copy
- exception: Remember whether message is multiline
- float: Update position of anchored windows first
- float: Fix some other crashes with :unhide or :all
- lua: Not using global value in vim.opt_global
- lua: Show error message when failing to set variable
- mouse: Click on 'statuscolumn' with 'rightleft'
- path: Accept special characters on Windows
- provider: Fix python3 provider cannot detect python3.12
- provider/pythonx: Import the correct module
- rpc: Fix race condition
- runtime: Add commentstring for D ftplugin
- statuscolumn: Update number hl for each screen line
- terminal: Check terminal size at end of screen update
- treesitter: Remove more double recursion
- ui: "resize -1" with cmdheight=0
- unhide: Close floating windows first
- unittests: Ignore __s128 and __u128 types in ffi
- tutor: Clarify the meaning of ✗ and ✓

BUILD SYSTEM!
- deps: Bump libmpack-lua to 1.0.11
- ci: fix mac release for Sonoma

NVIM v0.9.2

NVIM v0.9.1

NVIM v0.9.0

NVIM v0.8.3

NVIM v0.8.2

NVIM v0.8.1