RFR: Add Dockerfile, zero-dep reproducible builds

[Gavin Ray]

As title says, adds a Dockerfile that will fetch all necessary deps and build `jextract` for you on Ubuntu 22.10

It would be nice if some official JDK organization could put this on their Dockerhub, so that users could just do:


$ docker run --rm -it openjdk/jextract:latest


I've pushed it to my personal Dockerhub, so if anyone would like to test it out, you can use the README directions but prepend `gavinray/` before the image name:


$ echo "struct Foo { int a; long b; }; int use_foo(struct Foo foo);" >> sample.h

$ docker run --rm -it -v ${PWD}:/tmp/jextract \
    gavinray/jextract:latest \
    -I /tmp/jextract \
    --source \
    -l libfoo \
    --output /tmp/jextract/generated \
    --target-package com.example \

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Commit messages:
 - Add Dockerfile, zero-dep reproducible builds

Changes: https://git.openjdk.org/jextract/pull/74/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=74&range=00
  Stats: 75 lines in 2 files changed: 75 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jextract/pull/74.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/74/head:pull/74

PR: https://git.openjdk.org/jextract/pull/74