Allow arbitrary inline markdown syntax

Hi, thank you for making this!

I want to propose enabling arbitrary inline markdown syntax in caption text. (Related issue: #12)

I did it by passing captionText to MarkdownRenderer.renderMarkdown.

The current approach has at least two limitations:

renderMarkdown requires sourcePath to correctly process links, but I'm not aware how we can get sourcePath in the callback function passed to MutationObserver. This can affect how other link-related plugins (e.g. MathLinks, Strange New Worlds) work. Maybe we can address it by using MarkdownRenderChild, and trigger reloading every time a mutation occurs (but I've had no luck so far)
As for internal images, it cannot deal with caption text that contains internal links like ![[Pasted image 20230918180409.png|Compatible with [[MathLinks]]]]. So I had to make up a original notation << >> to avoid this: ![[Pasted image 20230918180409.png|Compatible with <<MathLinks>>]]. Obviously this isn't cool.

(Also, I'm currently passing the plugin instance to renderMarkdown's last parameter component, but it doesn't seem to be a good practice (https://github.com/obsidianmd/obsidian-releases/pull/2263#issuecomment-1711864829). I haven't found a proper way to do it yet.)

How do you like it?

Example:

Source:

## External link example

`![$\mathcal{A}$rb*itrary* **Inline** [[Markdown]] ==Syntax==! Compatible with [[MathLinks]]](https://github.com/RyotaUshio/obsidian-image-captions/raw/main/example.png)`

In this case, it's compatible with MathLinks because I CAN pass `sourcePath` to `renderMarkdown` in `externalImageProcessor`.

![$\mathcal{A}$rb*itrary* **Inline** [[Markdown]] ==Syntax==! Compatible with [[MathLinks]]](https://github.com/RyotaUshio/obsidian-image-captions/raw/main/example.png)

## Internal link example

`![[Pasted image 20230918180409.png|Compatible with <<MathLinks>>]]`

In this case, it's not compatible with MathLinks because I can't pass `sourcePath` to `renderMarkdown` in `MutationObserver`.

![[Pasted image 20230918180409.png|Incompatible with <<MathLinks>>]]

alangrainger / obsidian-image-captions

Allow arbitrary inline markdown syntax #15