refactor(core): rename core pkg dir to core

packages/core/src/composables/index.ts

@@ -0,0 +1,10 @@
+export { default as useHandle } from './useHandle'
+export { default as useKeyPress } from './useKeyPress'
+export { default as useZoomPanHelper } from './useZoomPanHelper'
+export { default as useWindow } from './useWindow'
+export { default as useVueFlow } from './useVueFlow'
+export { default as useDrag } from './useDrag'
+export { default as useNodeHooks } from './useNodeHooks'
+export { default as useEdgeHooks } from './useEdgeHooks'
+export { default as useEdge } from './useEdge'
+export { default as useNode } from './useNode'