feat: add decorations library with brace function

[RubixDev]

This PR adds a new CeTZ library called "Decorations". Currently it only contains one function, i.e. braces, but I thought other decorations may also be added to the same module in the future. For example, zig-zag and coiled lines, or more complex shapes like gears.

Here is a screenshot of the example I added to the manual:

A few points you may want to consider before merging:

• The brace function does not define a custom style root, and because it uses merge-path internally also doesn't even use the bezier styles. I think it would be better for users if they could set styles for all braces, also including the things that are currently direct function parameters (amplitude, pointiness, content-offset). I just don't have enough experience with CeTZ yet to implement that myself.
• The brace function takes a debug parameter. Should this maybe just respect the canvas's debug setting (if that is even possible)? It shows more specific and different information than the normal debug though.
• The brace function currently does no type and value checking of the parameters. Should some assertions be added?
• The brace function exposes anchors for all debug points. I guess this could potentially expose a bit too much of the internal structure and may lead to breaking changes for just slight internal refactors. The most important points are already exposed with appropriate names, so I would have no problem with removing these anchors.
• I just saw that there is a line-normal function in the util module, which could be used in two places instead of the _rotate-around function and may be faster or more accurate.
• The current description of the module in the manual is a bit meh, but I don't really know what to write there with only one function existing yet.

Also just for reference, this PR started out with me experimenting on the Typst Discord here.

[fenjalien]

This is really impressive nice work!

• Have a look at the other libs to see how they resolve their styles
• If you wrap the whole thing in a group and use a callback you can get ctx which has ctx.debug so you could attach it to that. You can keep the parameter anyway as it is cool to see.
• Have added a comment regarding type checking, main values to focus are coordinates. You can do it without ctx by using coordinate.resolve-system(...) which will just return a string of the coordinate type or panics if it is invalid.
• Don't worry about the debug anchors they're cool.
• If you can use something that aready exists in then yea, if not dw.
• Its alright.

Could you add a test for them? we don't have any guidlines but @johannes-wolf would be able to help if you need it.

[Beiri22]

That is exactly what I need; please, when you merge this PR, push it as new version to the package repo!

[johannes-wolf]

That is exactly what I need; please, when you merge this PR, push it as new version to the package repo!

Ok, will release 0.1.3 after this got merged.

[johannes-wolf]

This looks great! Cant wait to have this merged :)

[johannes-wolf]

LGTM.
I will add tests for this in a follow-up PR.

[johannes-wolf]

@Beiri22 Release PR: typst/packages#165