[Feature] SVG files: toggle between preview and editable source

[lukaszflorczak]

Problem

Opening an SVG gives me the rendered image only. To change anything I have to open the same file somewhere else, and opening it as code means losing the preview.

What I'd like

A toggle on SVG files to switch between the preview and the editable source, so both are one click apart.

Environment

Termic 0.28.1, macOS.

[simion]

Added in 89a7738.

An .svg now opens with the same source / split / preview toggle markdown files have, so the picture and the editable source are one click apart. Rather than building a second toggle, the shared parts (toolbar, split divider, and the rules that keep both panes mounted so your cursor and undo history survive a switch) moved out of the markdown pane into one component both use, so the two cannot drift apart later.

Two things beyond the literal ask that seemed worth doing:

The preview renders what is in the editor, not what is on disk. So in split view the picture updates as you type, before you save. Nothing is written until you hit save as usual.

Clicking an .svg in the file tree still shows the picture. SVG has its own remembered default (starting at preview), separate from markdown's, so this does not change for anyone who prefers to read markdown as source. Whichever mode you switch to is remembered for the next SVG.

One edge case: a very large SVG (over 2 MB) or one that is not valid UTF-8 cannot be opened in the text editor at all, and those used to render fine as an image. Those still render, the preview just falls back to reading the file from disk.

[simion]

This is live in v0.29.0, released today.