testsuite: add browser001 test for wasm ghci browser mode

This commit adds support for testing the wasm ghci browser mode in the
testsuite, as well as a simple first test case browser001 that makes
use of TH, JSFFI and browser-specific DOM API. See added note and
comments for details.

(cherry picked from commit ac70e643)
(cherry picked from commit f3e0f4bd)