Add `lslq` in `tronls` allowed subsolvers

[tmigot]

const tronls_allowed_subsolvers = [:cgls, :crls, :lslq, :lsqr, :lsmr]

Originally posted by @amontoison in #145 (comment)

[dpo]

The iterate norm is monotonic, but the residual is not monotonic in LSLQ. So I don't think you can just plug it into a trust-region method.