feat(core): Added Path.clean() method. Closes #3038 and #3056

This is a fix for bug #3038 which was investigated by @BenJamesBen
who also proposed a fix in PR #3056

However, after discussing the matter, we agreed it would be better
to have a generic method in core to guard against the issue of
spurious drawing operations.

This commit adds the `Path.clean()` method that does exactly that,
as well as its documentation.

markdown/dev/reference/api/path/clean/en.md

@@ -0,0 +1,61 @@
+---
+title: Path.clean()
+---
+
+The `Path.clean()` method removes spurious drawing operations from a path.
+
+A _spurious_ drawing operation is one that has no effect, but can still cause
+problems if left in place.  For example, a line from a given point to the same
+given point will not cause any problems as such, but can trip up things like
+path offset and other methods. For this reason, such drawing operations can be
+cleaned up with the `Path.clean()` method.
+
+As this method is called under the hood to guard against various scenarios
+where spurious segments could cause an issue, you should have no need to call
+this method yourself explicitly, but it's there if you need it.  path that you
+pass it.
+
+## Signature
+
+```js
+Path path.clean()
+```
+
+## Example
+
+<Example caption="Example of the Path.clean() method">
+```js
+({ Point, points, Path, paths, snippets, Snippet, part }) => {
+
+  points.A = new Point(10, 10)
+  points.B = new Point(10, 20)
+  points.C = new Point(10, 30)
+  points.D = new Point(90, 10)
+  points.E = new Point(90, 20)
+  points.F = new Point(90, 30)
+  
+  paths.a = new Path()
+    .move(points.A)
+    .line(points.C)
+    .line(points.B)
+    .line(points.B) // spurious op
+    .line(points.E)
+    .line(points.F)
+    .curve_(points.F, points.F) // another spurious op
+    .line(points.D)
+    .addClass('lining')
+
+  paths.b = paths.a
+    .clone()
+    .clean()
+    .addClass('interfacing')
+
+  paths.a.addText(`${paths.a.ops.length} ops in a`, 'center fill-lining')
+  paths.b.addText(`${paths.b.ops.length} ops in b`, 'center fill-note')
+    .attr('data-text-dy', 7)
+
+  return part
+}
+```
+</Example>
+

packages/core/src/path.mjs

@@ -166,6 +166,34 @@ Path.prototype.bbox = function () {
   return __bbbbox(bbs)
 }
 
+/**
+ * Returns this after cleaning out in-place path operations
+ *
+ * Cleaned means that any in-place ops will be removed
+ * An in-place op is when a drawing operation doesn't draw anything
+ * like a line from the point to the same point
+ *
+ * @return {Path} this - This, but cleaned
+ */
+Path.prototype.clean = function () {
+  const ops = []
+  for (const i in this.ops) {
+    const op = this.ops[i]
+    if (['move', 'close', 'noop'].includes(op.type)) ops.push(op)
+    else if (op.type === 'line') {
+      if (!op.to.sitsRoughlyOn(cur)) ops.push(op)
+    } else if (op.type === 'curve') {
+      if (!(op.cp1.sitsRoughlyOn(cur) && op.cp2.sitsRoughlyOn(cur) && op.to.sitsRoughlyOn(cur)))
+        ops.push(ops)
+    }
+    const cur = op?.to
+  }
+
+  if (ops.length < this.ops.length) this.ops = ops
+
+  return this
+}
+
 /**
  * Returns a deep copy of this path
  *
@@ -1117,6 +1145,7 @@ function __asPath(bezier, log = false) {
       new Point(bezier.points[2].x, bezier.points[2].y),
       new Point(bezier.points[3].x, bezier.points[3].y)
     )
+    .clean()
 }
 
 /**