Support rendering strikethrough text in markdown (#8287)

Just noticed strikethrough text handling was not implemented for the
following:

Chat

![image](https://github.com/zed-industries/zed/assets/53836821/ddd98272-d4d4-4a94-bd79-77e967f3ca15)

Markdown Preview

![image](https://github.com/zed-industries/zed/assets/53836821/9087635c-5b89-40e6-8e4d-2785a43ef318)

Code Documentation

![image](https://github.com/zed-industries/zed/assets/53836821/5ed55c60-3e5e-4fc2-86c2-a81fac7de038)

It looks like there are three different markdown parsing/rendering
implementations, might be worth to investigate if any of these can be
combined into a single crate (looks like a lot of work though).

Release Notes:

- Added support for rendering strikethrough text in markdown elements

Cargo.lock

@@ -7042,11 +7042,11 @@ dependencies = [
 
 [[package]]
 name = "pulldown-cmark"
-version = "0.9.3"
+version = "0.10.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "77a1a2f1f0a7ecff9c31abbe177637be0e97a0aef46cf8738ece09327985d998"
+checksum = "dce76ce678ffc8e5675b22aa1405de0b7037e2fdf8913fea40d1926c6fe1e6e7"
 dependencies = [
- "bitflags 1.3.2",
+ "bitflags 2.4.1",
  "memchr",
  "unicase",
 ]