CmdPal: Add settings to control which fallbacks are enabled (#40505)

This adds settings to each provider to allow us to control if individual
fallback items are enabled or not, regardless of the provider being
enabled.

This is relevant to _all the threads where disabling fallback commands
came up_

This just adds another section to each provider's settings page, with a
list of the fallback commands.

This also has nothing to do with the "top-level apps search", which is
not really a fallback command - it's its own thing.

Ref #38288. Doesn't close that, because this only controls
enable/disable, not ranking.

From here, we should be able to add a dedicated page in the SUI that
shows all the fallbacks across all providers. That's where we'll enable
the ordering.

src/modules/cmdpal/Microsoft.CmdPal.UI/Strings/en-us/Resources.resw

@@ -241,6 +241,10 @@ Right-click to remove the key combination, thereby deactivating the shortcut.</v
     <value>Commands</value>
     <comment>A section header for information about the app</comment>
   </data>
+  <data name="ExtensionFallbackCommandsHeader.Text" xml:space="preserve">
+    <value>Fallback commands</value>
+    <comment>A section header for information about the commands presented to the user when the search text doesn't exactly match the name of a command.</comment>
+  </data>
   <data name="ExtensionDisabledHeader.Text" xml:space="preserve">
     <value>This extension is disabled</value>
     <comment>A header to inform the user that an extension is not currently active</comment>