This eliminates much of the duplication between the two token hierarchies
by merging much of the fasta.Token hierarchy into the analyzer.Token.
* merge token hierarchies
* cleanup fasta.Token.copy()
* set preceedingComments field via constructor
* replace isBuiltInIdentifier --> type.isBuiltIn
* change all fasta.Token references to analyzer.Token
* move fasta.Token.value() implementation into analyzer.SimpleToken
R=scheglov@google.com
Review-Url: https://codereview.chromium.org/2890523002 .
Dan Rubel
278c7bfbeb