Adopt the ArgumentParser library for the command-line tools (#2653)

This transitions the Commands tools to use ArgumentParser instead 
of the TSC parser. The biggest change is that the tools are no 
longer subclasses of SwiftTool. Instead, each tool conforms to the
SwiftCommand protocol, which requires the shared options and creates
a SwiftTool instance after parsing.

Author: natecook1000

CMakeLists.txt

@@ -43,6 +43,7 @@ find_package(dispatch QUIET)
 find_package(Foundation QUIET)
 
 find_package(Yams CONFIG REQUIRED)
+find_package(ArgumentParser CONFIG REQUIRED)
 find_package(SwiftDriver CONFIG REQUIRED)
 
 add_subdirectory(Sources)

Package.swift

@@ -147,7 +147,7 @@ let package = Package(
         .target(
             /** High-level commands */
             name: "Commands",
-            dependencies: ["SwiftToolsSupport-auto", "Build", "PackageGraph", "SourceControl", "Xcodeproj", "Workspace", "XCBuildSupport"]),
+            dependencies: ["SwiftToolsSupport-auto", "Build", "PackageGraph", "SourceControl", "Xcodeproj", "Workspace", "XCBuildSupport", "ArgumentParser"]),
         .target(
             /** The main executable provided by SwiftPM */
             name: "swift-package",
@@ -263,11 +263,13 @@ if ProcessInfo.processInfo.environment["SWIFTPM_LLBUILD_FWK"] == nil {
 if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
     package.dependencies += [
         .package(url: "https://github.com/apple/swift-tools-support-core.git", .branch("master")),
+        .package(url: "https://github.com/apple/swift-argument-parser.git", .upToNextMinor(from: "0.3.0")),
         .package(url: "https://github.com/apple/swift-driver.git", .branch("master")),
     ]
 } else {
     package.dependencies += [
         .package(path: "./swift-tools-support-core"),
+        .package(path: "../swift-argument-parser"),
         .package(path: "../swift-driver"),
     ]
 }

Sources/Commands/CMakeLists.txt

@@ -8,8 +8,6 @@
 
 add_library(Commands
   APIDigester.swift
-  Completions+bash.swift
-  Completions+zsh.swift
   Describe.swift
   Error.swift
   GenerateLinuxMain.swift
@@ -24,6 +22,7 @@ add_library(Commands
   SymbolGraphExtract.swift
   WatchmanHelper.swift)
 target_link_libraries(Commands PUBLIC
+  ArgumentParser
   Build
   PackageGraph
   SourceControl