manuals: suppress excess use of "following" word

To simplify the style, replace "Following is" and "Following are"
by "here is" and "here are", sounding more natural.

In some cases, also go further by simplifying "Here are/is xxx"
by "xxx are/is" when the "are" or "is" are not two far at
the end of the sentence.

In some cases too, completely remove the sentence, when
it's redundant with the preceding title.

(From yocto-docs rev: 2539f1b9cbf9bdd40eff93c6522dc76133debed7)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
CC: Daniel Ammann <daniel.ammann@bytesatwork.ch>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

documentation/ref-manual/classes.rst

@@ -616,7 +616,7 @@ information about using :ref:`ref-classes-devshell`.
 The :ref:`ref-classes-devupstream` class uses
 :term:`BBCLASSEXTEND` to add a variant of the
 recipe that fetches from an alternative URI (e.g. Git) instead of a
-tarball. Following is an example::
+tarball. Here is an example::
 
    BBCLASSEXTEND = "devupstream:target"
    SRC_URI:class-devupstream = "git://git.example.com/example;branch=main"
@@ -1141,8 +1141,8 @@ Please keep in mind that the QA checks
 are meant to detect real or potential problems in the packaged
 output. So exercise caution when disabling these checks.
 
-Here are the tests you can list with the :term:`WARN_QA` and
-:term:`ERROR_QA` variables:
+The tests you can list with the :term:`WARN_QA` and
+:term:`ERROR_QA` variables are:
 
 -  ``already-stripped:`` Checks that produced binaries have not
    already been stripped prior to the build system extracting debug
@@ -3148,7 +3148,7 @@ information.
 The :ref:`ref-classes-uboot-sign` class provides support for U-Boot verified boot.
 It is intended to be inherited from U-Boot recipes.
 
-Here are variables used by this class:
+The variables used by this class are:
 
 -  :term:`SPL_MKIMAGE_DTCOPTS`: DTC options for U-Boot ``mkimage`` when
    building the FIT image.