[vscode-graphql-syntax] Syntax for markdown should re-use js embed rules

### Current Behavior
Currently, we have a markdown implementation that applies it's own logic for detecting graphql tags inside markdown blocks.

In LSP terms, that is a three times embedded language, haha! Vue and Svelte, markdown, all are examples of languages that embeds js/ts, which users expect to highlight embedded markdown for.

### Expected Behaviour

Any improvements to the javascript implementation should happen for markdown. We just need to tweak the grammar json files to do so.