Homogenize positive-definite criteria in GSF code

[rappoccio]

As described here there are two separate ways to check for positive-definiteness in the GSF code. To urgently fix the prompt reco, this was put through, but a proper solution is needed.

[cmsbuild]

A new Issue was created by @rappoccio .

@Dr15Jones, @perrotta, @dpiparo, @rappoccio, @makortel, @smuzaffar can you please review it and eventually sign/assign? Thanks.

cms-bot commands are listed here

[rappoccio]

assign @swagata87

[rappoccio]

assign @cms-sw/egamma-pog-l2

[swagata87]

assign egamma-pog

[cmsbuild]

New categories assigned: egamma-pog

@lfinco,@swagata87 you have been requested to review this Pull request/Issue and eventually sign? Thanks

[swagata87]

type egamma