[FIRRTL] Change FIRRTL Parser to Require Commas

[seldridge]

The FIRRTL spec changes to making commas mandatory. Previously, these were whitespace. While no changes are necessary to the FIRRTL parser in CIRCT (as it currently treats commas as whitespace and will parse a superset of the newly restricted FIRRTL), we should move towards aligning the parser with the spec.

Change the FIRRTL parser to start rejecting fun things like:

FIRRTL version 4.0.0
circuit ,Foo,,,,,,,:
  module ,,,,,,,,,Foo,,,:
    ,,,input,, a,,:UInt<1>
    ,,,output ,b,:,UInt<1>

    ,,,connect b a