Support import maps in Denops plugins

[lambdalisue]

Currently, import maps cannot be used for Denops plugins because Deno does not support dynamic import maps or multiple import maps.

• Support dynamic import maps denoland/deno#5791
• Dynamically generating import maps denoland/deno#6782

This limitation is quite inconvenient. To address this, we propose adding a transformation layer that substitutes @std/async with jsr:@std/async@^1.0.0 or any other mappings defined in an import_map.json file located in the parent directories of the Denops plugin.

The transformation layer could be implemented as an HTTP server, similar to deno-localfile-registry. Denops would import plugins via this server, ensuring that the appropriate import_map.json for each plugin is correctly applied.

Additional Context

• --import-map option seems inconsistent from imports or importMap field in deno.json denoland/deno#27539