issue #10820 Snippet in same file to share docs

[albert-github]

When having e.g.:

## \file

# [common_param_a]
#  @param a This is a common parameter that appears in many functions.
# [common_param_a]

## @brief This is a function.
#
# @snippetdoc example.py common_param_a
# @param b This is another parameter.
def function1(a, b):
    pass

or analogous in Fortran:

!> \file

! [ftn_common_param_a]
!  @param a This is a common parameter that appears in many functions.
! [ftn_common_param_a]

!> @brief This is a function.
!>
!> @snippetdoc this ftn_common_param_a
!> @param b This is another parameter.
subroutine ftn_function1(a, b)
    INTEGER a
    INTEGER b
end subroutine

we get warnings like:

example.py:4: warning: '\param' command is not allowed in section title, ending section title.

and in Fortran the ! appears in the output

Whilst in C++ the analogous example:

/// \file

/** @brief This is a function.
 *  @snippet{doc} this cpp2_common_param_a
 *  @param b This is another parameter. */
void cpp2_function1(int a, int b){}

/*  [cpp2_common_param_a]
 *  @param a This is a common parameter that appears in many functions.
 *  [cpp2_common_param_a]
*/

works OK, due to the rule

<DocBlock>"\\ilinebr "{B}*"*"/[^/]      {
                                          QCString indent;
                                          indent.fill(' ',computeIndent(yytext+8,yyextra->column));
                                          yyextra->docBlock << "\\ilinebr " << indent;
                                        }

added analogous rules for python and Fortran.

Example: example.tar.gz

(see also #10700 and #10702)