Fix ns detection for complex metadata

[yuhan0]

See clojure-emacs/cider#2821

Use clojure-forward-logical-sexp to reliably skip metadata instead of error-prone regex.

The previous variable clojure-namespace-name-regex is kept as obsolete in case it breaks other packages - can remove it directly if that's preferred.

One of the commented out TODO tests used a old metadata syntax #^{:bar true} which wasn't supported by clojure--looking-at-non-logical-sexp

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[bbatsov]

Nicely done!

[yuhan0]

Thanks! Just as another data point from the wild, the clojure.string ns form was being detected wrongly before due to the docstring containing "(ns ...":
https://github.com/clojure/clojure/blob/master/src/clj/clojure/string.clj#L14

With the changes in this PR it now works correctly :)