Allow arithmetic integer expressions in all places where previously
only integer literals were allowed.
The operators +, -, *, / and % are supported. Additionally, in field,
field_high, and padding specifications, the constants "word_size" and
"canonical" are available.
This enables more readable bitfield specifications without changing
any of the code and proof generation. Produces identical output to
before.
Signed-off-by: Gerwin Klein <gerwin.klein@proofcraft.systems>