fix(sdk): escape brackets in file paths with embedProject/openProject

[fvsch]

Frameworks such as Next.js and SvelteKit use square brackets in their file-based routing API. For instance a SvelteKit route may use this file path:

src/routes/hello/[...path]/+layout.ts

With the form posting method used by the embedProject and openProject methods, this currently gets turned into the following input name:

project[files][src/routes/hello/[...path]/+layout.ts]

Which trips up the StackBlitz backend.

This PR turns the [] characters in file paths, and only those characters, into their corresponding URI-escaped values. The StackBlitz backend will do the corresponding decoding. Note that we do not want to encodeURIComponent the full file path, because that would break backwards compatibility with StackBlitz Enterprise Edition.