This commit changes permission prompt to show that "import()" API
is requesting permissions.
Given "dynamic_import.js" like so:
```
import("https://deno.land/std@0.170.0/version.ts");
```
Before:
```
deno run dynamic_import.js
⚠️ ┌ Deno requests net access to "deno.land".
├ Run again with --allow-net to bypass this prompt.
└ Allow? [y/n] (y = yes, allow; n = no, deny) >
```
After:
```
deno run dynamic_import.js
⚠️ ┌ Deno requests net access to "deno.land".
├ Requested by `import()` API
├ Run again with --allow-net to bypass this prompt.
└ Allow? [y/n] (y = yes, allow; n = no, deny) >
```
This commit refactors several things in "runtime/permissions" module:
- splits it into "mod.rs" and "prompter.rs"
- adds "PermissionPrompter" trait with two implementations:
* "TtyPrompter"
* "TestPrompter"
- adds "before" and "after" prompt callback which can be used to hide
progress bar in the CLI (to be done in a follow up)
- "permissions_prompt" API returns "PromptResponse" enum, instead
of a boolean; this allows to add "allow all"/"deny all" functionality
for the prompt
