fix(doc): `deno doc --lint mod.ts` should output how many files checked (#21084)

As pointed out in https://github.com/denoland/deno/issues/21067 , it's
confusing that `deno doc --lint mod.ts` outputs the documentation to
stdout on success. Instead, it would be better if it outputted how many
files were checked similar to what `deno lint` does on success. It still
outputs the documentation if `--lint` or `--html` are provided so this
is non-breaking.

1 files changed, 5 insertions, 0 deletions

diff --git a/cli/tests/testdata/doc/lint_success.ts b/cli/tests/testdata/doc/lint_success.ts
new file mode 100644
index 000000000..42c44b2d7
--- /dev/null
+++ b/cli/tests/testdata/doc/lint_success.ts
@@ -0,0 +1,5 @@
+/** My test class. */
+export class Test {
+  /** My property. */
+  prop: string;
+}