fix(troika-three-text): fix changing text length in ThreeJS r117+

Fixes #69. This works around an issue introduced in Three r117 where a
given geometry uses the size of any InstancedBufferAttribute as a max
for `instanceCount`, and caches that for the lifetime of the geometry
even if the attribute is replaced with one of a different size.

It's unclear if this is a ThreeJS bug or a if our approach of "resizing"
by replacing the attribute is truly unsupported; the discussion in
mrdoob/three.js#19706 is ambiguous,
mrdoob/three.js#19595 implies it's not
allowed, and mrdoob/three.js#17418 implies it
should be allowed.

packages/troika-three-text/src/GlyphsGeometry.js

@@ -162,6 +162,14 @@ function updateBufferAttr(geom, attrName, newArray, itemSize) {
       attr.needsUpdate = true
     } else {
       geom.setAttribute(attrName, new InstancedBufferAttribute(newArray, itemSize))
+      // If the new attribute has a different size, we also have to (as of r117) manually clear the
+      // internal cached max instance count. See https://github.com/mrdoob/three.js/issues/19706
+      // It's unclear if this is a threejs bug or a truly unsupported scenario; discussion in
+      // that ticket is ambiguous as to whether replacing a BufferAttribute with one of a
+      // different size is supported, but https://github.com/mrdoob/three.js/pull/17418 strongly
+      // implies it should be supported. It's possible we need to
+      delete geom._maxInstanceCount //for r117+, could be fragile
+      geom.dispose() //for r118+, more robust feeling, but more heavy-handed than I'd like
     }
   } else if (attr) {
     geom.deleteAttribute(attrName)