It's not a particular common phrase and it's a little old-fashioned. It means the same thing as "I have never." It puts a little extra stress on the idea of "never." I have to mention one striking example of usage: in the song "Many a New Day," from the musical "Oklahoma," in which it is used half-a-dozen times. https://www.youtube.com/watch?v=ZmJnIr7ScTc The first use is a little after 1:17. Many a new face will please my eye, Many a new love will find me; Never have I once looked back to sigh over the romance behind me; Many a new day will dawn before I do! Many a light lad may kiss and fly, A kiss gone by is bygone. Never have I asked an August sky, "Where has last July gone?" Never have I wandered through the rye, wondering where has some guy gone; Many a new day will dawn before I do! Many a new face will please my eye, Many a new love will find me; Never have I once looked back to sigh over the romance behind me; Many a new day will dawn before I do!

In my life, I have never been so excited to see anyone. I have never been this glad to see anyone I have never been so excited to see anyone.

this is a grammar lesson which called "Inversion" the original sentence as you mentioned above is converted like this : I have never been so glad. In this case simply the place of auxiliary verb is changed with the subject. the purpose of this, here is to show and emphasis on the fact that, the subject is very surprised.

The two sentences are not the same. "Never have I been so glad" is like saying that this is the most glad I have ever been, or I have never been this glad before. "I have been so glad" could be used as such, "I have been so glad to be with you."