kernel: convert many C comments to C++ comments

[fingolfin]

Why? For the inline comments deal with in the first commit (made using a perl invocation) the reasoning is this: Adjusting comments like

    /* catch infix operations                                          */

or

    UInt                t1;             /* type of left  operand           */
    UInt                t2;             /* type of right operand           */
    ArithMethod2        func;           /* mod function                    */

to always fill exactly the correct number of columns is a major PITA. Failing to shorten such a comment also interacts badly with clang-format..

For multi-line comments, I usually also find it easier to come up with a uniform styling when using C++ comments; for multiline C comments, we have a plethora of ways to format them. Which of course isn't a serious problem on its own, except it adds mental load ("how should I format this comment??")

Note that this PR deliberately does not touch the big "block" comments of this kind (other than "fixing" some with "obvious" deviations):

/****************************************************************************
**
*F  SyRmdir( <name> )  . . . . . . . . . . . . . . .  remove directory <name>
*/

I actually also have a script converting those, but this may require more discussion and so I wanted to keep it seperate.

[ChrisJefferson]

this one not handled?

[fingolfin]

Aha, indeed. This is because of the T. We have to decide how to treat such comments. Presumably could be converted to // TODO: . Does that seems sensible?

Just to explain, the main part of this (in the first commit) was created using a very simple perl invocation. The idea is to take care of the 95% of "easy" cases in a fully automated way, to make it easy to rebase the PR if needed. Then the remaining cases may need some more manual work. Of course I can add more "automated" changes, but I'd like to keep each separate transformation as simple as possible.

[ChrisJefferson]

i'm happy for this to be merged as-is, and my comments to be dealt with later, just wanted to raise them as I checked to make sure nothing looked broken.

[fingolfin]

Ideally I'd like to get PR #5256 merged first, as it is easier to deal with resulting conflicts in this PR here (as most of the changes can be easily re-created by re-running a script.

[fingolfin]

This is now good to go from my POV