Add a specialized token factory

Add a specialized token factory

Our baseline parsing footprint is rather large. We can improve it
by looking at token component sizes and using distinct token classes.

Aside from CommonToken, which are using as fallbacks for text
handling, we introduce 4 specialized classes, three of them seeing
typical use.

Since these classes use smaller fields to hold lazy state, as well
as eliminate typical invariants, we end up saving around 39MiB (12%)
of AST size in a typical case from the field.

JIRA: YANGTOOLS-1128
Change-Id: I600ae6cbe755212e2d1a15ae3e6b369ed0b3b962
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>