Expand PlotLocator into a class

This centralizes the PlotLocator code (esp. the construction & accessors). It also allows just the PlotLocator to be passed to hasID - since the AtlasLocator is overkill for that call.

Change-Id: I424b2d075c40ed46219a623f0c99b3101bc7e043
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/282861
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
diff --git a/src/gpu/text/GrAtlasManager.cpp b/src/gpu/text/GrAtlasManager.cpp
index 47dae97..c91eab6 100644
--- a/src/gpu/text/GrAtlasManager.cpp
+++ b/src/gpu/text/GrAtlasManager.cpp
@@ -29,7 +29,7 @@
 
 bool GrAtlasManager::hasGlyph(GrMaskFormat format, GrGlyph* glyph) {
     SkASSERT(glyph);
-    return this->getAtlas(format)->hasID(glyph->fAtlasLocator);
+    return this->getAtlas(format)->hasID(glyph->fAtlasLocator.plotLocator());
 }
 
 // add to texture atlas that matches this format