Allow concatenation of string literals at compile time

[vlstill]

This gives wording to #1297, the compile-time concatenation of strings. The P4C part of this is p4lang/p4c#4856. The changes are relatively small, I hope I have not missed any more parts that mention that there are no string operations. Note that as stated here, it also allows string concatenation in @name, @deprecated and @noWarn pragmas. The last one has probably no use for it, but I think it is better to be consistent there.

Resolves #1297.

[vlstill]

Resulting PDF spec P4-16-spec.pdf.

[vlstill]

@jafingerhut, @jonathan-dilorenzo, @rcgoodfellow, any comments? I'd love for this one to get in before the next spec revision goes out.

[rcgoodfellow]

Mostly LGTM. Just a few nits.

[vlstill]

Thanks for the comments and sorry for the delayed response. I think I've fixed all the issues now.

[jafingerhut]

@vlstill Sorry for the inconvenience, but we have, after several months of planning, transitioned the P4 language specification source from Madoko to AsciiDoc. Thus most or all of your PRs will need to be updated so that they apply to that version. Hopefully this should be fairly straightforward, e.g. by looking at examples of how things like section headings, bullet items, etc. are marked up in the latest version of the file P4-16-spec.adoc

If you have questions on how to change things for AsciiDoc, feel free to ask. Note that creating a new PR with similar changes as this PR might be easier than updating this PR.

[vlstill]

@jafingerhut, no problem, I've refreshed the PR for the new asciidoc documentation.

[vlstill]

@jonathan-dilorenzo, @rcgoodfellow this was already discussed, now there is just updated wording in the new template, can we get this merged now?

[jaehyun1ee]

LGTM!

[jonathan-dilorenzo]

@jonathan-dilorenzo TAL at this and give comments or merge.