Help: Add SHELL, LINKER and host/device discussions to property docs

Section headings are also added for each common block to help guide
the reader and improve navigation.

Fixes: #21640

Help/command/DEVICE_LINK_OPTIONS.txt

@@ -1,3 +1,5 @@
+Host And Device Specific Link Options
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 .. versionadded:: 3.18
   When a device link step is involved, which is controlled by

Help/command/LINK_OPTIONS_LINKER.txt

@@ -1,3 +1,6 @@
+Handling Compiler Driver Differences
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 To pass options to the linker tool, each compiler driver has its own syntax.
 The ``LINKER:`` prefix and ``,`` separator can be used to specify, in a portable
 way, options to pass to the linker tool. ``LINKER:`` is replaced by the

Help/command/OPTIONS_SHELL.txt

@@ -1,3 +1,6 @@
+Option De-duplication
+^^^^^^^^^^^^^^^^^^^^^
+
 The final set of options used for a target is constructed by
 accumulating options from the current target and the usage requirements of
 its dependencies.  The set of options is de-duplicated to avoid repetition.