Add bindings for PDF tags

[tinchodias]

There is an API introduced in cairo v1.6.0 to add hyperlinks for a PDF surface. The bindings would be simple, and simple to use. See this example:

cairo_tag_begin (cr, CAIRO_TAG_LINK, "uri='https://cairographics.org'");
cairo_move_to (cr, 50, 50);
cairo_show_text (cr, "This is a link to the cairo website.");
cairo_tag_end (cr, CAIRO_TAG_LINK);

It is also possible to link to a local destination (in the same PDF), using another tag. More details on this API: https://www.cairographics.org/manual/cairo-Tags-and-Links.html

[tinchodias]

Bindings would be, at the lowest-level, adding 2 methods to AeCairoContext:

tagBegin: tagName attributes: attributesAsString

	self ffiCall: #(
		void
		cairo_tag_begin (
			self,
			char *tagName,
			char *attributesAsString ))

and:

tagEnd: tagName

	self ffiCall: #(
		void
		cairo_tag_end (
			self,
			char *tagName ))

those tag names can be in a new class AeCairoTag with 4 class-side methods.

Additionally, other higher-level methods could translate Pharo objects arguments to the attributesAsString that tagBegin: expects.