[Clang][Diagnostics] Use "structured binding" instead of "decomposition"

[zwuis]

P0615R0 changed the term "decomposition" to "structured binding". Some diagnostic messages were created before this paper. These messages should be updated using "structured binding" to avoid making users confused.

[tbaederr]

Good first issue?

[frederick-vs-ja]

We only need to change

• clang/include/clang/Basic/DiagnosticParseKinds.td,
• clang/include/clang/Basic/DiagnosticSemaKinds.td, and
• a lot of test files.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. Check that no other contributor is working on this issue. If someone is assigned to the issue or claimed to be working on it, ping the person. After one week without a response, the assignee may be changed.
2. Leave a comment indicating that you are working on the issue, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Yanzuo Liu (zwuis)

[P0615R0](https://wg21.link/p0615r0) changed the term "decomposition" to "structured binding". Some diagnostic messages were created before this paper. These messages should be updated using "structured binding" to avoid making users confused.

[sharma-sourabh3435]

Hi, I would like to work on this.

[shafik]

Hi, I would like to work on this.

Open a PR and then we can assign it to you

[rounakkumarsingh]

@sharma-sourabh3435 Reply if you ever stop working on it.

[sharma-sourabh3435]

@sharma-sourabh3435 Reply if you ever stop working on it.

I am currently working on this

[foxfromabyss]

Took the opportunity to work on the issue, seeing how a month passed after the last response. Haven't changed the code beyond the actual diagnostic messages as that seemed out of scope.
Despite tests being mentioned as something to be updated as well above, I haven't found any reference to "decomposition" or variants thereof in the test suite, other than class/function names.

Happy to receive any feedback regarding the PR.