[mlir][ods] Unify Attr/TypeDef and Operation Format Parsing

Part 2 of 3 of unifying the assembly formats of attributes/types and operations.The last patch that introduced attribute/type formats (D111594) factored out the format lexer entirely. This patch factors out most of the format parsers such that the attribute/type and op parsers only need to implement handling for specific elements.

Certain things could be factored better (element verification, 'seen' variables) but the primary goal of factoring is so that features can be used across both assembly formats.

Reviewed By: rriddle

Differential Revision: https://reviews.llvm.org/D117971