prevent invalid markup in generators

It is not allowed to render a button inside an <a> tag:

https://html.spec.whatwg.org/multipage/text-level-semantics.html#the-a-element

Therefore, we invert the order of the elements and nest a link inside a
button and forward any button clicks to the link.

Fixes #5770.
References #5814.

priv/templates/phx.gen.html/index.html.heex

@@ -1,9 +1,11 @@
 <.header>
   Listing <%= schema.human_plural %>
   <:actions>
-    <.link href={~p"<%= schema.route_prefix %>/new"}>
-      <.button>New <%= schema.human_singular %></.button>
-    </.link>
+    <.button phx-click={JS.dispatch("click", to: {:inner, "a"})}> 
+      <.link href={~p"<%= schema.route_prefix %>/new"}>
+        New <%= schema.human_singular %>
+      </.link>
+    </.button>
   </:actions>
 </.header>
 

priv/templates/phx.gen.html/show.html.heex

@@ -2,9 +2,11 @@
   <%= schema.human_singular %> <%%= @<%= schema.singular %>.id %>
   <:subtitle>This is a <%= schema.singular %> record from your database.</:subtitle>
   <:actions>
-    <.link href={~p"<%= schema.route_prefix %>/#{@<%= schema.singular %>}/edit"}>
-      <.button>Edit <%= schema.singular %></.button>
-    </.link>
+    <.button phx-click={JS.dispatch("click", to: {:inner, "a"})}>
+      <.link href={~p"<%= schema.route_prefix %>/#{@<%= schema.singular %>}/edit"}>
+        Edit <%= schema.singular %>
+      </.link>
+    </.button>
   </:actions>
 </.header>
 

priv/templates/phx.gen.live/index.ex

@@ -9,9 +9,11 @@ defmodule <%= inspect context.web_module %>.<%= inspect Module.concat(schema.web
     <.header>
       Listing <%= schema.human_plural %>
       <:actions>
-        <.link navigate={~p"<%= schema.route_prefix %>/new"}>
-          <.button>New <%= schema.human_singular %></.button>
-        </.link>
+        <.button phx-click={JS.dispatch("click", to: {:inner, "a"})}>
+          <.link navigate={~p"<%= schema.route_prefix %>/new"}>
+            New <%= schema.human_singular %>
+          </.link>
+        </.button>
       </:actions>
     </.header>
 

priv/templates/phx.gen.live/show.ex

@@ -10,9 +10,11 @@ defmodule <%= inspect context.web_module %>.<%= inspect Module.concat(schema.web
       <%= schema.human_singular %> <%%= @<%= schema.singular %>.id %>
       <:subtitle>This is a <%= schema.singular %> record from your database.</:subtitle>
       <:actions>
-        <.link navigate={~p"<%= schema.route_prefix %>/#{@<%= schema.singular %>}/edit?return_to=show"}>
-          <.button>Edit <%= schema.singular %></.button>
-        </.link>
+        <.button phx-click={JS.dispatch("click", to: {:inner, "a"})}>
+          <.link navigate={~p"<%= schema.route_prefix %>/#{@<%= schema.singular %>}/edit?return_to=show"}>
+            Edit <%= schema.singular %>
+          </.link>
+        </.button>
       </:actions>
     </.header>