Add clean.cmd, clean.ps1 and clean.sh (dotnet#11154)

- dotnet#10463

clean.cmd

@@ -0,0 +1,3 @@
+@ECHO OFF
+SETLOCAL
+PowerShell -NoProfile -NoLogo -ExecutionPolicy ByPass -Command "[System.Threading.Thread]::CurrentThread.CurrentCulture = ''; [System.Threading.Thread]::CurrentThread.CurrentUICulture = ''; try { & '%~dp0clean.ps1' %*; exit $LASTEXITCODE } catch { write-host $_; exit 1 }"

clean.ps1

@@ -0,0 +1,41 @@
+#requires -version 5
+
+<#
+.SYNOPSIS
+Clean this repository.
+
+.DESCRIPTION
+This script cleans this repository interactively, leaving downloaded infrastructure untouched.
+Clean operation is interactive to avoid losing new but unstaged files. Press 'c' then [Enter]
+to perform the proposed deletions.
+
+.EXAMPLE
+Perform default clean operation.
+
+    clean.ps1
+
+.EXAMPLE
+Clean everything but downloaded infrastructure and VS / VS Code folders.
+
+    clean.ps1 -e .vs/ -e .vscode/
+#>
+
+[CmdletBinding(PositionalBinding = $false)]
+param(
+    # Other lifecycle targets
+    [switch]$Help, # Show help
+
+    # Capture the rest
+    [Parameter(ValueFromRemainingArguments = $true)]
+    [string[]]$GitArguments
+)
+
+Set-StrictMode -Version 2
+$ErrorActionPreference = 'Stop'
+
+if ($Help) {
+    Get-Help $PSCommandPath
+    exit 0
+}
+
+git clean -dix -e .dotnet/ -e .tools/ -e src/SignalR/clients/ts/FunctionalTests/node_modules/ @GitArguments

clean.sh

@@ -0,0 +1,38 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+#
+# Functions
+#
+__usage() {
+    echo "Usage: $(basename "${BASH_SOURCE[0]}") <Arguments>
+
+Arguments:
+    <Arguments>...         Arguments passed to the 'git' command. Any number of arguments allowed.
+
+Description:
+    This script cleans the repository interactively, leaving downloaded infrastructure untouched.
+    Clean operation is interactive to avoid losing new but unstaged files. Press 'c' then [Enter]
+    to perform the proposed deletions.
+"
+}
+
+git_args=()
+
+while [[ $# -gt 0 ]]; do
+    case $1 in
+        -\?|-h|--help)
+            __usage
+            exit 0
+            ;;
+        *)
+            git_args[${#git_args[*]}]="$1"
+            ;;
+    esac
+    shift
+done
+
+# This incantation avoids unbound variable issues if git_args is empty
+# https://stackoverflow.com/questions/7577052/bash-empty-array-expansion-with-set-u
+git clean -dix -e .dotnet/ -e .tools/ ${git_args[@]+"${git_args[@]}"}