Get relative markdown links to work in VSCode hover

[pokey]

Links like https://github.com/cursorless-dev/cursorless/pull/1252/files#diff-23c8d079411ea2e84135122e2dbab063d6d496f727d28bd8aee977b7e39aaa83R35 don't work when you hover over the symbol in VSCode. Once microsoft/TypeScript#47718 is fixed, we'd like to get our relative links to work

See also:

• Remove hack to get relative markdown links in JSDocs to work with typedoc #1243
• https://github.com/cursorless-dev/cursorless/pull/1225/files#diff-759d5514ee12ed1657fe5757fb1631db90a7227d2140f98e390eefc62adb1b4d (note that this was rolled back, and the docusaurus hack was removed when we re-introduced the PR in Reintroduce stable hats #1252)
• Relative markdown links are not rewritten typedoc2md/typedoc-plugin-markdown#394
• `onBrokenMarkdownLinks` vs `onBrokenLinks` facebook/docusaurus#8613
• Provide way to link to other files from JSDoc comments  microsoft/TypeScript#47718
• Support local paths in hover MarkdownString microsoft/vscode#86564

Todo once this works

• Reintroduce png embeds in jsdocs (these were removed because they failed the link checker)
  • https://github.com/cursorless-dev/cursorless/pull/1523/files#diff-58435aea0c44b52640fa187e48191207bcb66c328f4cac025e9733522f0ad970R12
  • https://github.com/cursorless-dev/cursorless/pull/1523/files#diff-9d03de5cedda8405bfb8d25c22d1658886a532c85ac0f3f47f4d9fdb7f375543R12
  • https://github.com/cursorless-dev/cursorless/pull/1523/files#diff-c66527c13b8ada855bfac1d3da510cbeca92fb3d72c46c16ad94cf6f23f08b9bR11