[gimp-help] Add several missing layer related help ids

[Jacob Boerema <jboerema src gnome org>]

commit 1b42335ae058ac02f6d5e46f8b791b3fe6c9a98a
Author: Jacob Boerema <jgboerema gmail com>
Date:   Fri Oct 7 15:33:02 2022 -0400

    Add several missing layer related help ids
    
    (cherry picked from commit b00383d08e379d044a67619b71db8832a4eb0dfc)

 src/dialogs/layer-dialog.xml | 5 +++++
 src/menus/layer/new.xml      | 1 +
 2 files changed, 6 insertions(+)
---
diff --git a/src/dialogs/layer-dialog.xml b/src/dialogs/layer-dialog.xml
index 905788701..53a1f65a6 100644
--- a/src/dialogs/layer-dialog.xml
+++ b/src/dialogs/layer-dialog.xml
@@ -214,6 +214,7 @@
             <varlistentry id="gimp-layer-dialog-paint-mode-menu">
               <term>Mode</term>
               <listitem>
+                <anchor id="gimp-layer-mode"/>
                 <para>
                   The layer mode determines how the layer interacts with the
                   other layers. From the combo box you can access all the
@@ -225,6 +226,7 @@
             <varlistentry id="gimp-layer-dialog-opacity-scale">
               <term>Opacity</term>
               <listitem>
+                <anchor id="gimp-layer-opacity"/>
                 <indexterm>
                   <primary>Transparency</primary>
                   <secondary>Layer opacity</secondary>
@@ -263,6 +265,7 @@
                 </para>
                 <itemizedlist>
                   <listitem>
+                    <anchor id="gimp-layer-lock-pixels"/>
                     <para>
                       <emphasis role="bold">Lock pixels</emphasis>:  
                       When the button is pressed down, you cannot use any 
@@ -282,6 +285,7 @@
                     </figure>
                   </listitem>
                   <listitem>
+                    <anchor id="gimp-layer-lock-position"/>
                     <para>
                       <emphasis role="bold">Lock position and size</emphasis>:
                       This toggle button enables and disables protection of 
@@ -300,6 +304,7 @@
                     </figure>
                   </listitem>
                   <listitem>
+                    <anchor id="gimp-layer-lock-alpha"/>
                     <para>
                       <emphasis role="bold">Lock alpha channel</emphasis>: 
                       This toggle button controls the <quote>Lock</quote> 
diff --git a/src/menus/layer/new.xml b/src/menus/layer/new.xml
index 76b678266..11449a304 100644
--- a/src/menus/layer/new.xml
+++ b/src/menus/layer/new.xml
@@ -73,6 +73,7 @@
       <varlistentry>
         <term>Color tag</term>
         <listitem>
+          <anchor id="gimp-layer-color-tag"/>
           <para>
             If you click on one of these color buttons, the "Eye" icon box 
             of the created layer will have this color. This is interesting