fix(accordion)!: remove BaseAccordion

Closes #2612

fix(accordion): expand logic

refactor(accordion): prevent circular imports

.changeset/hip-coins-prove.md

@@ -0,0 +1,32 @@
+---
+"@patternfly/elements": major
+---
+`<pf-accordion>`: Removed `BaseAccordion*` classes, as well as static `isPanel`, `isHeader`, and `isAccordion` methods. Removed the optional `parentAccordion` parameter to `PfAccordion#expand(index)`. Renamed accordion event classes by adding the `Pf` prefix:
+
+**Before**:
+
+```js
+import {
+  AccordionHeaderChangeEvent
+} from '@patternfly/elements/pf-accordion/pf-accordion.js';
+
+addEventListener('change', function(event) {
+  if (event instanceof AccordionHeaderChangeEvent) {
+    // ...
+  }
+});
+```
+
+**After**:
+
+```js
+import {
+  PfAccordionHeaderChangeEvent
+} from '@patternfly/elements/pf-accordion/pf-accordion.js';
+
+addEventListener('change', function(event) {
+  if (event instanceof PfAccordionHeaderChangeEvent) {
+    // ...
+  }
+});
+```