Rework field and u32 comparison instructions

[Fumuran]

This small PR implements emulation of immediate values for field and u32 comparison instructions:

• U32Lt, U32Lte, U32Gt, U32Gte, U32Min, U32Max,
• Lt, Lte, Gt, Gte).

Instead of using additional *Imm(v) instruction variation, they are emulated with [Push(v), *instr*] array.

Related issue: #1374

[bobbinth]

Looks good! Thank you! I defer to @bitwalker to review the .lalrpop file.

[bitwalker]

LGTM!

Just one note for the future, for all of us: while this PR does simplify some parts of the assembler, which benefits us internally - the syntax tree data structures (Instruction in this instance) is part of our public API (one which the compiler uses, at a minimum). By removing conveniences from the AST and only providing them via the parser, it does impose additional burden on downstream producers of MASM ASTs to replicate whatever our parser is doing.

In this particular case, it's not really a problem, but I want to note the issue more generally, since I think it is a very easy at the moment to forget that the MASM parser is not the only way to produce MASM AST, and we could end up removing something that has actual usage/value beyond the assembler itself.

[Fumuran]

Right, I forgot about it honestly. Thank you @bitwalker for the admonition! Probably all subsequent assembler issues first should be discussed with you to make sure that changes in parser/AST won't create any problems for the compiler (or at least these problems could be easily fixed).