Move variables from connectedCallback to constructor in app.ts

I've noticed some long delays between when app.ts is created
and when connectedCallback is called, and I'm concerned that
because the variables aren't set until connectedCallback, we're
rendering things we don't need.

Not sure if this will actually make a difference in load times, but
I figured it can't hurt.

Bug: 329291869
Change-Id: I8d50d2b94186162dfbb185564bbf6f0b34010c60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5420540
Commit-Queue: Lauren Winston <lwinston@google.com>
Reviewed-by: Kristi Saney <kristislee@google.com>
Cr-Commit-Position: refs/heads/main@{#1282063}