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:
```ts
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:\
```
