man: reuse the shared "experimental" blurbs

The blurbs were added to be shared, but no sharing was actually
done.

Also, rename "singular"/"plural" to "option"/"options", so that we
can later have "component"/"components" and possibly other
variants.

The text were a bit different in various places, but I don't think
it was a useful distinction.

(cherry picked from commit 69dd30fddf2bbf358e05a632b0ef3383eb46b028)

man/experimental.xml

@@ -9,10 +9,10 @@
   <title/>
 
   <!-- for individual section(s) of a manpage -->
-  <para id="singular">This option is experimental and subject to change at any given moment without notice.
+  <para id="option">This option is experimental and subject to change at any given moment without notice.
   It will be stabilized and given a backward-compatibility guarantee in a future release.</para>
 
-  <para id="plural">These options are experimental and subject to change at any given moment without notice.
+  <para id="options">These options are experimental and subject to change at any given moment without notice.
   They will be stabilized and given a backward-compatibility guarantee in a future release.</para>
 
   <!-- for a whole manpage -->

man/systemd-measure.xml

@@ -26,12 +26,11 @@
     </cmdsynopsis>
   </refsynopsisdiv>
 
+  <xi:include href="experimental.xml" xpointer="component" />
+
   <refsect1>
     <title>Description</title>
 
-    <para>Note: this command is experimental for now. While it is likely to become a regular component of
-    systemd, it might still change in behaviour and interface.</para>
-
     <para><command>systemd-measure</command> is a tool that may be used to pre-calculate and sign the
     expected TPM2 PCR 11 values that should be seen when a Linux <ulink
     url="https://uapi-group.org/specifications/specs/unified_kernel_image/">UAPI.5 Unified Kernel Image

man/systemd-pcrlock.xml

@@ -34,12 +34,11 @@
     </cmdsynopsis>
   </refsynopsisdiv>
 
+  <xi:include href="experimental.xml" xpointer="component" />
+
   <refsect1>
     <title>Description</title>
 
-    <para>Note: this command is experimental for now. While it is likely to become a regular component of
-    systemd, it might still change in behaviour and interface.</para>
-
     <para><command>systemd-pcrlock</command> is a tool that may be used to analyze and predict TPM2 PCR
     measurements, and generate TPM2 access policies from the prediction which it stores in a TPM2 NV index
     (i.e. in the TPM2 non-volatile memory). This may then be used to restrict access to TPM2 objects (such as

man/systemd-report.xml

@@ -30,12 +30,11 @@
     </cmdsynopsis>
   </refsynopsisdiv>
 
+  <xi:include href="experimental.xml" xpointer="component" />
+
   <refsect1>
     <title>Description</title>
 
-    <para><emphasis>Note: this command is experimental for now. While it is likely to become a regular
-    component of systemd, it might still change in behaviour and interface.</emphasis></para>
-
     <para><command>systemd-report</command> requests metrics from the system and writes them to
     standard output.</para>
   </refsect1>