Merge #19438 from 3N4N/fix/pwsh

Reverts #16271
Fixs #15913

Problem:
Since #16271, `make_filter_cmd` uses `Start-Process` cmdlet to execute the user
provided shell command for `:%!`. `Start-Process` requires the command to be
split into the shell command and its arguments. This was implemented in #19268
by parsing (splitting the user-provided command at the first space) which didn't
handle cases such as --
  - commands with escaped space in their filepath
  - quoted commands with space in their filepath

Solution: Use piping.

The total shell command formats (excluding noise of unimportant parameters):

1. Before #16271
    ```powershell
    pwsh -C "(shell_cmd) < tmp.in | 2>&1 Out-File -Encoding UTF8 <tmp.out>"
    # not how powershell commands work
    ```
2. Since #16271
    ```powershell
    pwsh -C "Start-Process shell_cmd -RedirectStandardInput <tmp.in> -RedirectStandardOutput <tmp.out>"
    # doesn't handle executable path with space in it
    # doesn't write error to <tmp.out>
    ```
3. This PR
    ```powershell
    pwsh -C "& { Get-Content <tmp.in> | & 'path\with space\to\shell_cmd.exe' arg1 arg2 } 2>&1 | Out-File -Encoding UTF8 <tmp.out>"
    # also works with forward slash in the filepath
    # also works with double quotes around shell command
    ```

After this PR, the user can use the following formats:

    :%!c:\Program` Files\Git\usr\bin\sort.exe
    :%!'c:\Program Files\Git\usr\bin\sort.exe'
    :%!"c:\Program Files\Git\usr\bin\sort.exe"
    :%!"c:\Program` Files\Git\usr\bin\sort.exe"

They can even chain different commands:

    :%!"c:\Program` Files\Git\usr\bin\sort.exe" | sort.exe -r

But if they want to call a stringed executable path, they have to provide the
Invoke-Command operator (&). In fact, the first stringed executable path also
needs this & operator, but this PR adds that behind the scene.

    :%!"c:\Program` Files\Git\usr\bin\sort.exe" | sort.exe -r | & 'c:\Program Files\Git\usr\bin\sort.exe'

## What this PR solves

- Having to parse the user-provided bang ex-command (for splitting into shell
  cmd and its args).
- Removes a lot of human-unreadable `#ifdef` blocks.
- Accepting escaped spaces in executable path.
- Accepting quoted string of executable path.
- Redirects error and exception to tmp.out (exception for when `wrong_cmd.exe
  not found`)

## What this PR doesn't solve

- Handling wrongly escaped path to executable, which the user may pass because
  of cmdline tab-completion. #18592

## Edge cases
- (Not handled) If the user themself provides the `&` sign (means `call
  this.exe` in powershell)
- (Not handled) Use `-Encoding utf8` parameter for `Get-Content`?
- (Handled) Doesn't write to tmp.out if shell command is not found.
    - fix: use anonymous function (`{wrong_cmd.exe}`).

## Changes other than `make_filter_cmd()` function

- Encoding for piping to external executables. See BOM-less UTF8:
  https://github.com/PowerShell/PowerShell/issues/4681

test/functional/helpers.lua

@@ -562,16 +562,16 @@ function module.set_shell_powershell(fake)
     assert(found)
   end
   local shell = found and (iswin() and 'powershell' or 'pwsh') or module.testprg('pwsh-test')
-  local set_encoding = '[Console]::InputEncoding=[Console]::OutputEncoding=[System.Text.Encoding]::UTF8;'
+  local set_encoding = '[Console]::InputEncoding=[Console]::OutputEncoding=[System.Text.UTF8Encoding]::new();'
   local cmd = set_encoding..'Remove-Item -Force '..table.concat(iswin()
-    and {'alias:cat', 'alias:echo', 'alias:sleep'}
+    and {'alias:cat', 'alias:echo', 'alias:sleep', 'alias:sort'}
     or  {'alias:echo'}, ',')..';'
   module.exec([[
     let &shell = ']]..shell..[['
     set shellquote= shellxquote=
     let &shellcmdflag = '-NoLogo -NoProfile -ExecutionPolicy RemoteSigned -Command ]]..cmd..[['
     let &shellpipe = '2>&1 | Out-File -Encoding UTF8 %s; exit $LastExitCode'
-    let &shellredir = '-RedirectStandardOutput %s -NoNewWindow -Wait'
+    let &shellredir = '2>&1 | Out-File -Encoding UTF8 %s; exit $LastExitCode'
   ]])
   return found
 end

test/functional/vimscript/system_spec.lua

@@ -642,12 +642,12 @@ describe('shell :!', function()
     if iswin() then
       feed(':4verbose %!sort /R<cr>')
       screen:expect{
-        any=[[Executing command: .?Start%-Process sort %-ArgumentList "/R" %-RedirectStandardInput .* %-RedirectStandardOutput .* %-NoNewWindow %-Wait]]
+        any=[[Executing command: .?& { Get%-Content .* | & sort /R } 2>&1 | Out%-File %-Encoding UTF8 .*; exit $LastExitCode"]]
       }
     else
       feed(':4verbose %!sort -r<cr>')
       screen:expect{
-        any=[[Executing command: .?Start%-Process sort %-ArgumentList "%-r" %-RedirectStandardInput .* %-RedirectStandardOutput .* %-NoNewWindow %-Wait]]
+        any=[[Executing command: .?& { Get%-Content .* | & sort %-r } 2>&1 | Out%-File %-Encoding UTF8 .*; exit $LastExitCode"]]
       }
     end
     feed('<CR>')