Publish org.processing.core.pdf to maven Central

[avinxshKD]

Adds Maven Central publishing configuration to the PDF library.

• Added maven-publish plugin
• Added publishing block for local app repository
• Added mavenPublishing block with POM metadata
• Follows same pattern as preprocessor module

Part of #1403

[avinxshKD]

@Stefterv hey started with PDF since it was the easiest.
Let me know if this looks good and I'll work on Net/SVG next. thanks

[Stefterv]

please set the coordinates like in my PR

[Stefterv]

version is available as a variable here so you can use the exact line as in my pr and only replace the library name

[Stefterv]

Thanks @avinxshKD I added a few comments ;)

[avinxshKD]

Thanks @avinxshKD I added a few comments ;)

sure was already on it thanks and welcome :)

[avinxshKD]

@Stefterv Updated the coordinates and removed the signing checkk. and
hve skipped the optional migration for this PR to keep it focused on just enabling publishing. Happy to look into a shared plugin in a follow-up refactor for all libraries at once, what do you say?

[avinxshKD]

Ready for another look.

[Stefterv]

The coordinates still need to be fixed, the version should be equal to the processing version, not the version from the library.properties

[avinxshKD]

@Stefterv hve updated the version to use rootProject.version so it matches the Processing version as requested

[Stefterv]

Hi @avinxshKD, it appears to me that you are overly relying on AI for making your changes, please take a look at this.
If not, please copy the coordinates line directly from my pr, only changing the library name