[svg] Expand SkSVGIRI type

This CL adds a type enum to SkSVGIRI that will eventually be used to
distinguish between local fragments ('#frag-id'), non-local fragments
('/path/to/file.png') and data URIs ('data:image/png;base64,...').

To do so required a bit of refactoring of other types that previously
treated IRIs as basic strings. There are no functional changes in this
CL.

Change-Id: I8bf426f77c0779890bce74d2d243c09617f024c8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/360601
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Tyler Denniston <tdenniston@google.com>
diff --git a/modules/svg/src/SkSVGText.cpp b/modules/svg/src/SkSVGText.cpp
index c571c30..b405a72 100644
--- a/modules/svg/src/SkSVGText.cpp
+++ b/modules/svg/src/SkSVGText.cpp
@@ -351,7 +351,7 @@
 
 SkSVGTextContext::PathData::PathData(const SkSVGRenderContext& ctx, const SkSVGTextPath& tpath)
 {
-    const auto ref = ctx.findNodeById(tpath.getHref().fIRI);
+    const auto ref = ctx.findNodeById(tpath.getHref());
     if (!ref) {
         return;
     }