Powershell: Fix CA2014: Stackalloc in loops

[rjmholt]

We currently suppress warnings of CA2014 in parts of the build. stackallocs in loops can cause stack overflows, so we need to refactor our code to fix this.

See:

https://github.com/PowerShell/PowerShell/blob/78d0d0e3065d946a1f17cc97cf29b94c12ce9c9f/src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleControl.cs#L2579

https://github.com/PowerShell/PowerShell/blob/78d0d0e3065d946a1f17cc97cf29b94c12ce9c9f/src/Microsoft.PowerShell.ConsoleHost/host/msh/ConsoleHostUserInterface.cs#L308

https://github.com/PowerShell/PowerShell/blob/78d0d0e3065d946a1f17cc97cf29b94c12ce9c9f/src/Microsoft.PowerShell.Commands.Management/commands/management/Process.cs#L787-L788

Suppression added in https://github.com/PowerShell/PowerShell/pull/13530

[iSazonov]

Only first case has real cycle.

[rjmholt]

We should work to factor out the loops that are not loops in these cases as well. For example, the do { } while (false); examples sorely need to be turned into methods

[daxian-dbw]

Both first and second are real loops, no?

[iSazonov]

For 1 case. StackAlloc is used only (1) ~for large output~, (2) if new line is needed, (3) once on last iteration - so we could add comment that it is safe to suppress.

For 2 case. We can move StackAlloc out the cycle.

For 3 case. We can remove the cycle and replace break-s with return-s.

[rjmholt]

It strikes me that in case 1 we just need a buffer -- we could allocate outside of the loop and simply reuse the buffer space within the loop. I imagine that's the intent of the warning anyway.

[iSazonov]

We could put all after line 2570 after the while cycle - it output a tail once.