std: add ignore parser for std/prettier

[axetroy]

ignore parser to parse ignore files like .gitignore/.npmignore/.prettierignore

Because it parses .prettierignore in the std/prettier

deno/std/prettier/main.ts

Lines 479 to 486 in c6bb3d5

	async function resolveIgnoreFile(filepath: string): Promise<string[]> {
	const raw = new TextDecoder().decode(await Deno.readFile(filepath));
	return raw
	.split("\n")
	.filter((v: string) => !!v.trim() && v.trim().indexOf("#") !== 0)
	.map(v => v);
	}

so I think it can be isolated

[ry]

LGTM