feat: support the all tag to enable every rule

[bartlomieju]

Refs #1244.

Adds a special all tag to filtered_rules: when the requested tag set
contains all, every rule matches regardless of its own tags. This lets a
configuration opt into the complete rule set with

{ "lint": { "rules": { "tags": ["all"] } } }

instead of enumerating every rule under include. It composes with the
existing exclude list to drop individual rules, e.g. tags: ["all"] +
exclude: ["no-explicit-any"].

This is the deno_lint-side primitive only. Two related ideas from the issue
are intentionally out of scope here and can build on top of this:

• tag-level negation (tags: ["all", "-fresh"]) — needs the config layer in
  the Deno CLI to map the negated tag onto excludes;
• user-defined custom tags.

Adds tests for all alone (returns every rule) and all + exclude.

[bartlomieju]

Verdict: LGTM — correct and tested. Recommend merge (public-behavior change, so flagging rather than auto-merging; needs green CI / rebase).

Correctness — good

• tags_set.contains("all") || rule.tags().iter().any(...) short-circuits to include every rule when all is present, and composes correctly with exclude (applied downstream) — both paths are covered by the added tests (all → get_all_rules().len(), and all + exclude → len() - 1 with the excluded code absent).
• contains("all") on the HashSet<String> resolves via Borrow<str>, so no allocation for the check. The || any(...) ordering also means the common all case avoids the per-tag scan.

Minor

• all is now effectively a reserved tag name. No current rule uses it, but worth a one-line note in the doc comment that all is reserved, so a future rule doesn't accidentally define a real all tag.
• Scope is correctly limited to the deno_lint primitive; tag-negation (-fresh) and custom tags are appropriately deferred to the CLI config layer, as you note.

Perf: neutral/slightly better (short-circuit on all).

Housekeeping: public API/behavior addition → maintainer sign-off (your own PR). mergeable: UNKNOWN → rebase.

No changes requested. Good to merge once CI is green.