System.CommandLine docs update (#46594)

* Updating docs to beta5: symbols, syntax, getting started guide

* Updating docs to beta5: termination, middleware, completions, binding

* Updating docs to beta5: help customization

* move "design guidance" to a dedicated doc, introduce new paragraphs: symbols and naming

* join syntax and "define commands", simplify the descriptions and just briefly mention features that are not expected to be used frequently like Recursive or Hidden symbols

* improve getting started tutorial: start it with bare minimum sample that does not use invocation at all, then use help to explain what invocation is and what it provides

* update Help customization based on our recent changes

* the separation of parsing and invocation

* simplify parsing and validation doc, add config doc, polish other docs

* beta5 migration guide

---------

Co-authored-by: Jeff Handley <[email protected]>
Co-authored-by: Genevieve Warren <[email protected]>
Co-authored-by: Jon Sequeira <[email protected]>

Author: 4 people

.openpublishing.redirection.fundamentals.json

@@ -168,6 +168,34 @@
             "source_path_from_root": "/docs/fundamentals/networking/httpclient.md",
             "redirect_url": "/dotnet/fundamentals/networking/http/httpclient"
         },
+        {
+            "source_path_from_root": "/docs/standard/commandline/customize-help.md",
+            "redirect_url": "/dotnet/standard/commandline/how-to-customize-help"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/define-commands.md",
+            "redirect_url": "/dotnet/standard/commandline/syntax#commands"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/dependency-injection.md",
+            "redirect_url": "/dotnet/standard/commandline/migration-guide-2.0.0-beta5#invocation"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/handle-termination.md",
+            "redirect_url": "/dotnet/standard/commandline/how-to-parse-and-invoke#process-termination-timeout"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/model-binding.md",
+            "redirect_url": "/dotnet/standard/commandline/how-to-parse-and-invoke"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/use-middleware.md",
+            "redirect_url": "/dotnet/standard/commandline/migration-guide-2.0.0-beta5#configuration"
+        },
+        {
+            "source_path_from_root": "/docs/standard/commandline/tab-completion.md",
+            "redirect_url": "/dotnet/standard/commandline/how-to-enable-tab-completion"
+        },
         {
             "source_path_from_root": "/docs/fundamentals/networking/httpclient-guidelines.md",
             "redirect_url": "/dotnet/fundamentals/networking/http/httpclient-guidelines"

docs/fundamentals/toc.yml

@@ -934,22 +934,25 @@ items:
             href: ../standard/commandline/index.md
           - name: Get started tutorial
             href: ../standard/commandline/get-started-tutorial.md
-          - name: Command-line syntax
+          - name: Command-line syntax overview
             href: ../standard/commandline/syntax.md
-          - name: Define commands
-            href: ../standard/commandline/define-commands.md
-          - name: Model binding
-            href: ../standard/commandline/model-binding.md
-          - name: Tab completion
-            href: ../standard/commandline/tab-completion.md
-          - name: Dependency injection
-            href: ../standard/commandline/dependency-injection.md
-          - name: Customize help
-            href: ../standard/commandline/customize-help.md
-          - name: Handle termination
-            href: ../standard/commandline/handle-termination.md
-          - name: Use middleware
-            href: ../standard/commandline/use-middleware.md
+          - name: How to
+            expanded: true
+            items:
+            - name: Parse and invoke the result
+              href: ../standard/commandline/how-to-parse-and-invoke.md
+            - name: Customize parsing and validation
+              href: ../standard/commandline/how-to-customize-parsing-and-validation.md
+            - name: Configure the parser
+              href: ../standard/commandline/how-to-configure-the-parser.md
+            - name: Enable and customize tab completion
+              href: ../standard/commandline/how-to-enable-tab-completion.md
+            - name: Customize help
+              href: ../standard/commandline/how-to-customize-help.md
+          - name: Design guidance
+            href: ../standard/commandline/design-guidance.md
+          - name: Migration guide to 2.0.0-beta5
+            href: ../standard/commandline/migration-guide-2.0.0-beta5.md
       - name: File and stream I/O
         items:
           - name: Overview