[migrated] Rewrite lexer and parser

[twiggler]

Note

Migrated from fox-it/dissect.cstruct#146 by @twiggler.
Original author: @Schamper

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Closes #85, partially #142, and will make #86 and #138 a lot easier to implement. Fixes #149.

This PR will (finally) replace the shoddy C syntax parser I originally wrote many moons ago, when I discovered the existence of re.Scanner and ran with it. This PR aims to add a somewhat decent lexer and separate parser. I'm still not a compsci 1337coder, so this is just what I came up with (with some help) and definitely not a textbook implementation. All feedback is welcome.

• New lexer
• New C syntax parser that utilizes the new lexer
• Expression parser re-uses the new lexer
• Reworked how sizeof works in the expression parser, and added offsetof

The new parser has made changing parsing behavior a lot easier. As such, this PR already makes the following changes:

• The new parser is slightly stricter, requiring proper semicolon endings for example. We'll need to fix this in any dissect code that has this.

• An important semantic change is how named nested structures are handled. In my infinite wisdom, I originally figured that named nested structures do not "exist" in the top level scope. That's not true, so now named nested structures get properly registered with the cstruct instance:

struct a {
    struct b {
        ...
    };
};

// Will register both `a` and `b`

• Another important change is how we deal with struct { ... } name;. We used to parse this first as an anonymous struct, then capture name as the structure type name. That's not strictly correct, name is a variable of an anonymous unnamed struct, so we now treat it as such. We don't error on this, but rather we silently ignore name and skip until we reach a ;
• typedef enum ... is now allowed
• Probably some other things I'm forgetting

This probably warrants a major version bump, so maybe good to pair this with #114, #144 and what we discussed in #142.

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Migration notes

• Package: dissect.cstruct
• Original base branch: main