RFR: Update jextract/panama branch to track JDK 22

[Maurizio Cimadamore]

On Thu, 15 Jun 2023 09:47:30 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

> This PR contains some initial changes to enable jextract support for the latest Panama repo (and JDK 22 in general).
> 
> It contains the usual updates to source, build and readme files (e.g. to replace jdk21 with jdk22).
> 
> On top of that there are some changes to support the latest API changes in the Panama repo such as:
> * removal of implicit sequence layout factory
> * renaming of XYZUtf8String -> XYZString

src/main/resources/org/openjdk/jextract/impl/resources/RuntimeHelper.java.template line 27:

> 25: import static java.lang.foreign.Linker.*;
> 26: import static java.lang.foreign.ValueLayout.*;
> 27: import static java.lang.Long.MAX_VALUE;

In principle, this is not required. But one test was failing as it was declaring a struct called "Long" :-)

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PR Review Comment: https://git.openjdk.org/jextract/pull/123#discussion_r1230750669