Also, trim some whitespace and group one rule better.
Also, fix a stray closing parenthesis in the JSON syntax,
and add the missing slash to the possible escaped characters.
(Reference: https://www.json.org/json-en.html.)
Also, improve the ending of multiline strings in the Rust syntax.
A backslash should not be allowed inside a quoted string unless
it is used to escape another character.
This fixes https://savannah.gnu.org/bugs/?61389.
Bug existed since each of these syntaxes was introduced.
(Awk and Fortran do not know include files with names between
angled brackets, so those regexes are dropped in the bargain.)
Quoted strings cannot start within another quoted string and end after
that other string has ended. Therefore single-quoted and double-quoted
strings should (as much as possible) be colorized by a single rule, so
that overlapping colorations are avoided.
(This also fixes a double typo in the PHP syntax (\. --> \\.) that has
been there since the PHP syntax was added in 2008, commit 90ee8ee4.)
This fixes https://savannah.gnu.org/bugs/?61387.
Bug existed since each of these syntaxes was introduced,
the oldest ones around 2006, a few others around 2015.
The one that got it right was the Lua syntax from 2011.
Within a bracket expression, the backslash is not special,
so it does not need to be escaped.
The double backslashes within brackets were found with:
grep -o '\[[^][]*\\\\[^][]*\]' syntax{,/extra}/*rc
Also, incorporate the square brackets into some bracket expressions
by listing the closing bracket first, saving a separate regex for
those two brackets.
In many places a carriage return is not valid whitespace and should
thus not be colored as such. In some of these places a vertical tab
or form feed is maybe valid whitespace, but it would be ugly or even
wrong to color them because they are not part of the subsequent
comment or keyword.
This fixes https://savannah.gnu.org/bugs/?60456.
