Auto merge of #13771 - noritada:feature/release-notes-on-github-releases, r=lnicola

Add xtask for publishing release notes in Markdown on GitHub Releases from a changelog in AsciiDoc

This PR provides `xtask publish-release-notes` to convert a changelog written in AsciiDoc to Markdown and update descriptions (release notes) of a corresponding entry on GitHub Releases.

This AsciiDoc parser is not capable of processing every AsciiDoc document, but I have surveyed a set of existing changelog entries and have confirmed that the following notations used can be converted properly. In the future, I would like to improve the parser to accept any AsciiDoc.  Alternatively, the parser could be moved out of the project.

Your feedback would be appreciated!

Closes #13191

### Supported AsciiDoc syntax

many occurrences
- [x] documentation header
- [x] section header
- [x] `*`-prefixed basic unordered single level list item
- [x] list continuation using `+`
- [x] block image macro `image::...[]` with empty alt
- [x] block image macro `image::...[]` with non-empty alt
- [x] block video marco `video::...[]` with `options=loop`
- [x] inline hard line break `+`
- [x] inline custom macro `commit:...[]`
- [x] inline custom macro `release:...[]`
- [x] inline custom macro `pr:...[]`
- [x] inline unconstrained bold text `**...**`
- [x] inline constrained monospace ``` `...`  ```

[thisweek/_posts/2019-07-24-changelog-0.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/tree/src/thisweek/_posts#:~:text=2019%2D07%2D24%2Dchangelog%2D0.adoc)
- [x] paragraphs
- [x] mixture of `*` and `-` for unordered list item prefix
- [x] inline external link `https://...[]`

[thisweek/_posts/2020-01-13-changelog-7.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/tree/src/thisweek/_posts#:~:text=2020%2D01%2D13%2Dchangelog%2D7.adoc)
- [x] list item with multiline principal text with indent
- [x] inline image macro `image:...[]`

[thisweek/_posts/2020-03-02-changelog-14.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/blob/src/thisweek/_posts/2020-03-02-changelog-14.adoc)
- [x] empty lines between list items
- [x] nested unordered list item with `**`
- [x] inline macro `kbd:[...]`

[thisweek/_posts/2020-03-16-changelog-16.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/blob/src/thisweek/_posts/2020-03-16-changelog-16.adoc)
- [x] `[source]`-prefixed listing

[thisweek/_posts/2020-04-06-changelog-19.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/blob/src/thisweek/_posts/2020-04-06-changelog-19.adoc)
- [x] list item with multiline principal text without indent
- [x] `[source,lang]`-prefixed listing
- [x] `.`-prefiexed ordered list item
- [x] list item immediately after list continuation paragraph without an empty line in between

[thisweek/_posts/2020-04-20-changelog-21.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/blob/src/thisweek/_posts/2020-04-20-changelog-21.adoc)
- [x] title line for block image

[thisweek/_posts/2020-12-21-changelog-56.adoc](https://github.com/rust-analyzer/rust-analyzer.github.io/blob/src/thisweek/_posts/2020-12-21-changelog-56.adoc)
- [x] block video `video::...[]` with `options="autoplay,loop"`

1 files changed, 4 insertions, 3 deletions

diff --git a/docs/dev/README.md b/docs/dev/README.md
index 4ac75b4bbfd..cdab6b09928 100644
--- a/docs/dev/README.md
+++ b/docs/dev/README.md
@@ -200,7 +200,7 @@ Look for `fn benchmark_xxx` tests for a quick way to reproduce performance probl
 
 ## Release Process
 
-Release process is handled by `release`, `dist` and `promote` xtasks, `release` being the main one.
+Release process is handled by `release`, `dist`, `publish-release-notes` and `promote` xtasks, `release` being the main one.
 
 `release` assumes that you have checkouts of `rust-analyzer`, `rust-analyzer.github.io`, and `rust-lang/rust` in the same directory:
 
@@ -231,8 +231,9 @@ Release steps:
    * create a new changelog in `rust-analyzer.github.io`
 3. While the release is in progress, fill in the changelog
 4. Commit & push the changelog
-5. Tweet
-6. Inside `rust-analyzer`, run `cargo xtask promote` -- this will create a PR to rust-lang/rust updating rust-analyzer's subtree.
+5. Run `cargo xtask publish-release-notes <CHANGELOG>` -- this will convert the changelog entry in AsciiDoc to Markdown and update the body of GitHub Releases entry.
+6. Tweet
+7. Inside `rust-analyzer`, run `cargo xtask promote` -- this will create a PR to rust-lang/rust updating rust-analyzer's subtree.
    Self-approve the PR.
 
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