read/xcoff: initial support.

[EsmeYi]

This patch adds a skeleton for reading XCOFF, which now can parses FileHeader/Sections/Symbols.
Comments are welcome.

[philipc]

As part of this, can you add some simple test files to https://github.com/gimli-rs/object-testfiles, and add tests here for the objdump example output. We'll also want readobj support and associated test too, but that's fine to leave for another PR.

[philipc]

At a high level, this looks great, and thanks for working on it. I'll wait until you've finished before doing a detailed review.

[EsmeYi]

The PR is ready for review now and the format will be clean in next commit.
@philipc @ecnelises Thanks for your review and look forward to your more comments.
The resource of test files are added to gimli-rs/object-testfiles#4.

[philipc]

Please add a command to build with only the xcoff format feature in CI:

object/.github/workflows/rust.yml

Lines 40 to 44 in ef9c666

	- run: cargo build --no-default-features --features read_core,write_core,coff
	- run: cargo build --no-default-features --features read_core,write_core,elf
	- run: cargo build --no-default-features --features read_core,write_core,macho
	- run: cargo build --no-default-features --features read_core,pe
	- run: cargo build --no-default-features --features read_core,wasm

[philipc]

It's okay if you want to leave some of this work for future PRs, but please add TODO comments to indicate that support is missing.

[philipc]

Just a few small things to fix and then I think this is ready to merge.

[philipc]

You'll also need to add the 32-bit files in gimli-rs/object-testfiles#4 and wait for it to be merged so that this PR can update it.

[EsmeYi]

Addressed comments.
@philipc Thank you for your patient review.

[philipc]

Can you include testfiles in the PR as well?

[philipc]

Thanks!