refactor: VectorStoreIndex: use TransformerComponent to calc embeddings (#721)

README.md

examples/multimodal/load.ts

packages/core/e2e/fixtures/embeddings/OpenAIEmbedding.ts

packages/core/src/embeddings/MultiModalEmbedding.ts

packages/core/src/embeddings/types.ts

packages/core/src/indices/vectorStore/index.ts