Limitations of `path()` basic shape

[estelle]

The required <string> is a single SVG Path string encompassed in quotes with numeric values representing pixel units.

The path page should include the above and following information:

While the path() function allows reuse of the SVG path syntax to define more arbitrary shapes than allowed by more specialized shape functions, it requires writing a path as a single string (which is not compatible with, for example, building a path piecemeal with var() and inherits a number of limitations from SVG, such as implicitly only allowing the px unit.

_Originally posted by @estelle in https://github.com/mdn/content/pull/33446#discussion_r1599064232_

[dipikabh]

path() is not supported in the shape-outside property:

• https://developer.mozilla.org/en-US/docs/Web/CSS/basic-shape/path#browser_compatibility
• https://developer.mozilla.org/en-US/docs/Web/CSS/shape-outside#browser_compatibility

This needs to be explicitly mentioned in both path() and shape-outside pages.

The following updates are especially needed on the shape-outside page:

• Remove use of path() in shape-outside from the Syntax examples.

• Update description of <basic-shape> in Values, which says path() is supported in spec level 2:

  The float area is computed based on the shape created by of one of inset(), circle(), ellipse(), polygon() or, as added in the level 2 specification, path().

  There's no mention of it in https://drafts.csswg.org/css-shapes-2/#shape-outside-property.