feat: import.meta.filename and import.meta.dirname

[bartlomieju]

This commit adds import.meta.filename and import.meta.dirname APIs.

These APIs return string representation of filename and containing dirname.
They are only defined for local modules (modules that have file:/// scheme).

Example:

console.log(import.meta.filename, import.meta.dirname)

Unix:

$ deno run /dev/my_module.ts
/dev/my_module.ts /dev/

Windows:

$ deno run C:\dev\my_module.ts
C:\dev\my_module.ts C:\

[ry]

lgtm