Add custom section sample and enable CI test

[TianlongLiang]

No description provided.

[Copilot]

Pull request overview

This PR adds a new custom-section sample demonstrating embedding an external payload into a Wasm custom section and retrieving/printing it from the host via wasm_runtime_get_custom_section, and wires the sample into CI so it’s built and executed (Wasm + AoT).

Changes:

• Add a new samples/custom-section sample (host app + wasm app + build/run scripts) for custom-section payload resolution via handle-based native APIs.
• Add documentation entries for the new sample.
• Update multiple GitHub Actions workflows to build/run the sample in CI, including AoT builds that preserve the custom section.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
samples/custom-section/wasm-apps/custom_section_payload.s	Defines a .custom_section.demo section and includes an external payload via .incbin.
samples/custom-section/wasm-apps/custom_section_payload.bin	Sample payload content to embed into the Wasm custom section.
samples/custom-section/wasm-apps/custom_section.c	Wasm-side demo entrypoint importing host APIs to resolve and print the custom section.
samples/custom-section/src/native_impl.c	Host native implementations to resolve a section name to a handle and print its bytes.
samples/custom-section/src/main.c	Host executable wiring runtime init, loading the Wasm module, and calling run_demo.
samples/custom-section/run.sh	Helper script to run the sample (Wasm or AoT).
samples/custom-section/build.sh	Builds the host app + Wasm module and optionally an AoT artifact preserving custom sections.
samples/custom-section/README.md	Sample documentation and usage instructions.
samples/custom-section/CMakeLists.txt	CMake project definition enabling WAMR_BUILD_LOAD_CUSTOM_SECTION.
samples/custom-section/.gitignore	Ignores the sample’s out/ directory.
samples/README.md	Adds the new sample to the samples index.
.github/workflows/nightly_run.yml	Builds/runs the new sample (Wasm + AoT) in nightly CI.
.github/workflows/compilation_on_macos.yml	Builds/runs the new sample (Wasm + AoT) in macOS CI.
.github/workflows/compilation_on_android_ubuntu.yml	Builds/runs the new sample (Wasm + AoT) in Android-on-Ubuntu CI.

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[Copilot]

The .section directive looks syntactically incomplete: .section .custom_section.demo,"",@ ends with @ but no section type. With clang/LLVM integrated assembler this is likely to error out or create an unexpected section. Specify an explicit section type (and any required flags) so the payload reliably lands in a .custom_section.demo section across toolchains.

Suggested change

	.section .custom_section.demo,"",@
	.section .custom_section.demo,"",@progbits

[TianlongLiang]

The Wasm assembler requires the three-part .section
name,"flags",@ syntax but doesn't accept any ELF section type after the @.