Add support for loading mermaid via esm module

[maxbrokman]

Fixes #70

Changes

• Bump default mermaid version to 10.0.2
• Add support for loading mermaid via an ESM module when requested mermaid version is >= 10
• Breaking Change: Loading mermaid directly through extra_javascript is no longer possible for version >= 10. This probably requires readme changes not included in this PR. It may be possible for users to include a simple JS file that imports mermaid via esm here instead.

Context

From mermaid v10 onwards mermaid is only distributed as an ESM module. See Mermaid #3590 for discussion on this change.

Users will probably notice this problem if they are following the readme recommended way of loading the latest version of mermaid through extra_javascript as including https://unpkg.com/mermaid/dist/mermaid.min.js resolves to e.g https://unpkg.com/mermaid@10.0.2/dist/mermaid.min.js which does not exist.

Looking around other projects this seems to be a common issue for libraries including mermaid.

To resolve this mermaid must now be explicitly imported through e.g

<script type="module">
import mermaid from "https://unpkg.com/mermaid@10.0.2/dist/mermaid.esm.min.mjs"
mermaid.initialize()
</script>

To achieve this this PR makes several changes:

• Bump default mermaid version to 10.0.2 (latest at time of writing)
• Split mermaid lib locations constants into pre and post 10 version to account for difference in locations
• Wrap mermaid lib info in a small value object that also tracks mermaid style (js or esm)
• Change resolution of mermaid location to make use of the above
• Change mermaid loader to user <script src="..."> or <script type="module"> as appropriate.

[fralau]

Thanks a lot for your contribution.

Could you describe in detail the problem you wanted to solve (what is esm, etc.), and how you solved it?

[maxbrokman]

Ah very sorry @fralau I have sent this to the wrong upstream! Was originally intending to review internally before pushing here but I will update the description shortly

[fralau]

Thanks a lot. I believe the right thing to do would be to open an issue to start the discussion and then, when needed the pull request. Looking forward!

[maxbrokman]

@fralau have now provided a description, sorry about that

[fralau]

I did my own implementation (to guarantee compatibility with earlier versions). Released in 1.0.0.

[flowolf]

this is not yet pushed to pypi - is this planned?