Make PDF highlighting work as expected also in absence of `:linenos:`

Method at 347f15ca2 was overly complicated, due to not enough
understanding of LaTeX package fancyvrb's innards.

sphinx/texinputs/sphinx.sty

@@ -853,8 +853,7 @@
 \newcommand*{\sphinxVerbatimEnvironment}{\gdef\FV@EnvironName{sphinxVerbatim}}
 % serves to implement line highlighting and line wrapping
 \newcommand\sphinxFancyVerbFormatLine[1]{%
-  \expandafter\sphinx@verbatim@checkifhl
-    \expandafter{\the\numexpr\value{FancyVerbLine}-\spx@verbatim@linedelta}%
+  \expandafter\sphinx@verbatim@checkifhl\expandafter{\the\FV@CodeLineNo}%
   \ifin@
      \sphinxVerbatimHighlightLine{#1}%
   \else
@@ -876,8 +875,6 @@
           \strut #1\strut}%
 }%
 \newcommand\sphinxVerbatimFormatLineNoWrap[1]{\hb@xt@\linewidth{\strut #1\hss}}%
-\def\sphinx@FancyVerbCodesHook
-   {\FV@SetLineNo\edef\spx@verbatim@linedelta{\the\value{FancyVerbLine}}}%
 \g@addto@macro\FV@SetupFont{%
     \sbox\sphinxcontinuationbox {\spx@opt@verbatimcontinued}%
     \sbox\sphinxvisiblespacebox {\spx@opt@verbatimvisiblespace}%
@@ -933,15 +930,11 @@
   % Allow breaks at special characters using \PYG... macros.
     \sphinxbreaksatspecials
   % Breaks at punctuation characters . , ; ? ! and / (needs catcode activation)
-    \expandafter\def\expandafter\sphinx@FancyVerbCodesHook\expandafter
-                   {\sphinx@FancyVerbCodesHook\sphinxbreaksviaactive}%
+    \fvset{codes*=\sphinxbreaksviaactive}%
   \else % end of conditional code for wrapping long code lines
     \let\sphinxVerbatimFormatLine\sphinxVerbatimFormatLineNoWrap
   \fi
   \let\FancyVerbFormatLine\sphinxFancyVerbFormatLine
-  % hook into \FancyVerbCodes to recover at first code line the numbering offset
-  \expandafter\def\expandafter\FancyVerbCodes\expandafter
-      {\FancyVerbCodes\sphinx@FancyVerbCodesHook}%
   % go around fancyvrb's check of \@currenvir
   \let\VerbatimEnvironment\sphinxVerbatimEnvironment
   % go around fancyvrb's check of current list depth