RFR: Add jextract guide [v5]

[Jorn Vernee]

On Fri, 12 Apr 2024 13:16:16 GMT, Nir Lisker <nlisker at openjdk.org> wrote:

>> Jorn Vernee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Phrasing
>>   
>>   Co-authored-by: Maurizio Cimadamore <54672762+mcimadamore at users.noreply.github.com>
>
> doc/GUIDE.md line 185:
> 
>> 183: 
>> 184: ```java
>> 185: // mylib_h.java
> 
> Assuming the class name options wasn't specified (if you want to mention that, though not important).

Don't think it's that important to mention. The comment is mostly there for consistency, as the text above already says that this is the class that jextract generates.

> doc/GUIDE.md line 200:
> 
>> 198: static wrapper method (1).
>> 199: 
>> 200: The parameter types and return type of this method depend on the carrier types of the
> 
> Is the reader supposed to know what a "carrier type" is? Can a link be given to an explanation if one exists in FFM maybe?

'carrier type` is indeed an FFM concept. I've added a link to `FunctionDescriptor::toMethodType` which explains how these are derived.

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PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1565790719
PR Review Comment: https://git.openjdk.org/jextract/pull/231#discussion_r1565789199