AM 6 doesn't recognize custom templates and partials

Reproduction steps

1. Git clone the AM external repository:$ git clone ssh://git@stash.forgerock.org:7999/openam/am-external.git
2. Check out the relevant branch. For example, 6.0.0$ cd am-external
   $ git checkout releases/6.0.0
   $ cd openam-ui

Modify the XUI code as follows while using this excerpt from the 5.5 doc as a guide https://backstage.forgerock.com/docs/am/5.5/ui-customization-guide/#d1661e408 
3A cd to the directory that the Fonts, images, partials, and other resources are provided in {{src/main/resources/}}for me in a 6.0 env and using the path as am-external this is 
/home/forgerock/GitHome/am-external/openam-ui/openam-ui-ria/src/main/resources/themes/dark/partials/login
3B. Add the following to the file _Password.html

<hr />

After modification the _Password.html should look look like this

<!--

  Copyright 2015-2017 ForgeRock AS. All Rights Reserved

  Use of this code requires a commercial software license with ForgeRock AS.

  or with one of its affiliates. All use shall be exclusively subject

  to such license between the licensee and ForgeRock AS.

-->

<hr />

<label for="" class="aria-label sr-only separator">

    <span></span>

</label>

<input type="password"

      id=""

      name="callback_"

      class="form-control input-lg"

      placeholder=""

      value=""

      data-validator="required"

      required

      data-validator-event="keyup"

      autofocus>

What this will do is create a horizontal line that renders above password fields on login pages, as displayed here

https://backstage.forgerock.com/docs/am/5.5/ui-customization-guide/images/xui-dark-theme-partial.png

Save the file

Next I edited the mappings in /home/forgerock/GitHome/am-external/openam-ui/openam-ui-ria/src/main/js/config/ThemeConfiguration.js to make the dark theme the default theme for all user logins

mappings: [

  { theme: "fr-dark-theme" }

Next ensure that the current directory is openam-ui
for example /home/forgerock/GitHome/am-external/openam-ui/

Set your Maven options:
export MAVEN_OPTS=-Xmx512m
Build the customizations using the following command
mvn clean install

After the build completed  I changed directory to the build directory, for ex /home/forgerock/GitHome/am-external/openam-ui/openam-ui-ria/build

copied the entire contents of files and directories in the build directory to $CATALINA_HOME/webapps/openam/XUI

which for me is /home/forgerock/apache-tomcat-8.5.16/webapps/openam/XUI/

cp -r /home/forgerock/GitHome/am-external/openam-ui/openam-ui-ria/build/*  /home/forgerock/apache-tomcat-8.5.16/webapps/openam/XUI/

With the server stopped remove the openam.war file in /home/forgerock/apache-tomcat-8.5.16/webapps/openam.war

cd to the directory /home/forgerock/apache-tomcat-8.5.16/webapps/openam/

jar cvf ../openam.war *

cd /home/forgerock/apache-tomcat-8.5.16/webapps/

rm -rf openam

cd to the tomcat work directory, for ex /home/forgerock/apache-tomcat-8.5.16/work/Catalina/localhost

rm -rf openam

start up tomcat with the following command

sh /home/forgerock/apache-tomcat-8.5.16/bin/catalina.sh
clear browser cache/cookies 

access openam login page

for example

http://openam6.example.com:8080/openam/XUI/#login/

Observed that the horizontal line that renders above password fields on login pages is not present, as shown in this screenshot

Confirmed that the edits made in the src in _Password.html are present in the openam deployment on tomcat

 cat /home/forgerock/apache-tomcat-8.5.16/webapps/openam/XUI/themes/dark/partials/login/_Password.html

<!--

  Copyright 2015-2017 ForgeRock AS. All Rights Reserved

  Use of this code requires a commercial software license with ForgeRock AS.

  or with one of its affiliates. All use shall be exclusively subject

  to such license between the licensee and ForgeRock AS.

-->

<hr />

<label for="" class="aria-label sr-only separator">

    <span></span>

</label>

<input type="password"

      id=""

      name="callback_"

      class="form-control input-lg"

      placeholder=""

      value=""

      data-validator="required"

      required

      data-validator-event="keyup"

      autofocus>