Update Github CI, docker setup and documentation to run on Ubuntu 24.04 with clang-20 and gcc-14

[anupsdf]

What:

Update Github CI, docker setup and documentation to run on Ubuntu 24.04 with clang-20 and gcc-14

Why:

Since stellar-core packages would be produced for Ubuntu 22.04 (jammy) and 24.04 (noble) with clang-20 moving forward, we would like to switch our Github CI to run on the new leading OS version of Ubuntu.

• Update Github actions runner to build with clang-20
• Update docker setup script and docs
• Drop support for Ubuntu 20.04 focal
• Update documentation
• Switch to corresponding gcc/g++ v14. Noble comes with gcc/g++ version 14 while jammy comes with 12. We could get gcc/g++ 13 on Jammy with PPA dependency. Which version should we recommend in our documentation? Currently, I have set Github CI to run gcc/g++ v14 since we run on GHA runner on Ubuntu 24.04.
• Run clang-format-20. Bunch of files have format changes due to this. Refer to clang-format20 style options

[Copilot]

Pull Request Overview

This PR updates the GitHub CI workflow to use Ubuntu 24.04 with clang-19 instead of Ubuntu 22.04 with clang-12, aligning the CI environment with the package distribution targets for stellar-core.

Key changes:

• Upgrades Ubuntu runner versions from 22.04 to 24.04
• Updates clang toolchain from version 12 to version 19
• Removes the dedicated clang-19 static analysis workflow

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
.github/workflows/clang-19-static-analysis.yml	Removes the entire dedicated clang-19 static analysis workflow file
.github/workflows/build.yml	Updates Ubuntu versions, clang toolchain to version 19, and adds format check skip

[MonsieurNicolas]

Not sure where the overall work to migrate to the right toolchain for Ubuntu 22.04 is tracked.
If this is the PR, you also need to update a few places, including https://github.com/stellar/stellar-core/blob/master/docker/Dockerfile.testing and https://github.com/stellar/stellar-core/tree/master/.devcontainer (grep for mentions of clang).

There is also the question of which version of gcc/g++ to reference in guides etc.

[anupsdf]

Not sure where the overall work to migrate to the right toolchain for Ubuntu 22.04 is tracked. If this is the PR, you also need to update a few places, including https://github.com/stellar/stellar-core/blob/master/docker/Dockerfile.testing and https://github.com/stellar/stellar-core/tree/master/.devcontainer (grep for mentions of clang).

There is also the question of which version of gcc/g++ to reference in guides etc.

I can use this PR to track the overall migration including the documentation. Will also include gcc/g++ updates here.

[MonsieurNicolas]

you may want to tweak the clang-format config to avoid spurious reformatting (usually it's because they add new config flags or change defaults).
You may be able to get a hint of what is going on by diffing the effective config with: clang-format -dump-config > .clang-format and tweak lines that changed and/or review what those configs do https://clang.llvm.org/docs/ClangFormatStyleOptions.html

[anupsdf]

you may want to tweak the clang-format config to avoid spurious reformatting (usually it's because they add new config flags or change defaults). You may be able to get a hint of what is going on by diffing the effective config with: clang-format -dump-config > .clang-format and tweak lines that changed and/or review what those configs do https://clang.llvm.org/docs/ClangFormatStyleOptions.html

Thanks for the tip! Here are the three categories of formatting changes I looked into but the conclusion is that we could tackle them in a followup PR to not clutter this one. Let me know what you think.

1. I am having a hard time tracking down which setting adds a space between closing parenthesis and opening curly brackets. I will keep looking at different combination of settings.
   () {};

2. In v12 we had AlwaysBreakAfterReturnType: AllDefinitions. In v20 they have replaced it with BreakAfterReturnType which has few options but they all modify a bunch of files and clutter this PR.
   I am inclining towards BreakAfterReturnType: ExceptShortType option which would break after return type based on PenaltyReturnTypeOnItsOwnLine with exception of short return types but we could discuss in a followup.

3. Optionally, switching BraceWrapping:BeforeLambdaBody to true would break the { of lambda functions onto a new line. But its something we could discuss as a followup issue as well.

[graydon]

Nice! Handful of mostly doc nits. I don't really care what happens with the formatting.

[jacekn]

How will you deal with version strings such as 24.1.1-2874.5a7035d49.noble~notforprod ?

[anupsdf]

I think in a future clean up we should have RUN_TAG also passed in along with the DISTRO so we can append the them to the stellar-core-version.