[AMORO-3531] Drop support for java8

[turboFei]

Why are the changes needed?

Close #3531

This PR removes support for Java 8 across the project. Reasons:
Java 8 is end-of-life and no longer receives public updates or security patches.
Modern libraries and frameworks increasingly require Java 11+.
Dropping Java 8 simplifies code maintenance and allows use of newer language features and APIs.
Improves compatibility with current cloud and container environments, which default to Java 11 or higher.

Brief change log

• Remove GA and deprecate Java8

How was this patch tested?

• Add some test cases that check the changes thoroughly including negative and positive cases if possible

• Add screenshots for manual tests if appropriate

• Run test locally before making a pull request

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 28.94%. Comparing base (17b68d0) to head (a403e20).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #3899      +/-   ##
============================================
+ Coverage     28.82%   28.94%   +0.11%     
- Complexity     3838     3847       +9     
============================================
  Files           625      631       +6     
  Lines         50514    50722     +208     
  Branches       6455     6496      +41     
============================================
+ Hits          14560    14680     +120     
- Misses        34928    34985      +57     
- Partials       1026     1057      +31     

Flag	Coverage Δ
core	28.94% <ø> (+0.11%)	⬆️

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[xxubai]

Should we drop support for Java8 in the next release? @zhoujinsong @baiyangtx @klion26

[turboFei]

is there an ETA for next release?

[zhoujinsong]

I am okay to drop JDK8 in the next version, if it keeps us from uprading the iceberg version.

[klion26]

As we have not deprecated JDK8 in 0.8.x, maybe we need to deprecate the jdk8 in 0.9.x and remove it in the version after 0.9.x(0.10.x or 1.0.x ). If we want to remove the JDK8 support more quickly, maybe we can make an earlier release for this.

[turboFei]

maybe we can make an earlier release for this.

+1. In my view, the legacy burden of JDK 8 has become a hindrance to the advancement of the community.

[github-actions]

This pull request has been marked as stale due to 30 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@amoro.apache.org list. Thank you for your contributions.

[czy006]

As we have not deprecated JDK8 in 0.8.x, maybe we need to deprecate the jdk8 in 0.9.x and remove it in the version after 0.9.x(0.10.x or 1.0.x ). If we want to remove the JDK8 support more quickly, maybe we can make an earlier release for this.

The removal of support for JDK8 has been approved through voting on the mailing list. I am in favor of this decision. Moving forward, with support for V3 or higher versions, we can no longer maintain compatibility with JDK8. It's time to bid farewell to it.