docs: reporting-issues: streamline process and solve a FIXME

This series bundle a few patches that piled up for Documentation/admin-guide/reporting-issues.rst. The main changes are these:

* patch 2/5: tones down 'test vanilla mainline' a little and mention that
vendor kernel might be find in some cases if they are close to vanilla. Gets rid of a "FIXME" box.

* patch 5/5: creates a streamlined process for users wanting to report
regressions within a stable and longterm kernel series. The existing process is too demanding, complicated and takes too much time for this case. I didn't CC the stable maintainers here, they need to review the whole document anyway once the last few details have been sorted out.

Patch 1/5 are just small fixes I wanted to keep separated. Patch 3/4 and 4/5 are mainly there to make the diff in the last patch of this series easier to read in the review phase. They can easily be squashed into the patches that follow them.

v3:
* add patch to fix a typo and an existing style-issue that came up during review that until now handled separately
* add related patch that tones down 'test vanilla mainline' a bit
* add another patch to make the diff easier to read

v2: https://lore.kernel.org/linux-doc/[email protected]/
* initial version, starting straight with v2 to avoid confusion, as one of the patches was submitted earlier already

Thorsten Leemhuis (5):
docs: reporting-issues.rst: fix small typos and style issues
docs: reporting-issues.rst: tone down 'test vanilla mainline' a little
docs: reporting-issues.rst: reorder some steps
docs: reporting-issues.rst: duplicate sections for reviewing purposes
docs: reporting-issues.rst: improved process esp. for stable
regressions

 .../admin-guide/reporting-issues.rst          | 832 ++++++++++--------
 1 file changed, 471 insertions(+), 361 deletions(-)

base-commit: a8f2a68e42d19e6fc1e0eb6eaef548ef07b19d75

2.30.2