Workers’ compensation — Medical benefits — Causation — Break in causal chain — Exposure — Action arising out of employer/carrier’s termination of medical treatment fifteen years after parties had entered into a broad stipulation in which the employer/carrier accepted compensability of work exposure to contaminants which caused breathing problems in employees of the building, and accepted liability for “building related illness associated with indoor air quality problems” — Judge of compensation claims’ denial of employee’s claims for medical care and costs was not supported by competent substantial evidence where, although physician who conducted employer/carrier’s independent medical evaluation testified that employee had been misdiagnosed, IME physician declined to testify that “building related illness” was not the major contributing cause of employee’s need for ongoing treatment, and no evidence was introduced by employer/carrier that employee’s symptoms changed since the date of the joint stipulation or that unrelated conditions or symptoms had arisen since exposure was accepted as compensable