feat(dom): allow plugins to modify element metadata

src/context/index.ts

src/context/source.ts

src/dom/htmlelement.spec.ts

src/dom/htmlelement.ts

src/meta/element.ts

src/meta/index.ts

src/meta/table.ts

src/parser/__snapshots__/parser.spec.ts.snap

src/parser/parser.spec.ts

src/parser/parser.ts

src/shim.ts