auxtools debug server: expression evaluation

[willox]

The changes for the language server are minimal. This will require shipping version 2.0.0 of the debug server: https://github.com/willox/auxtools/releases/tag/debug-v2.0.0 (use https://github.com/willox/auxtools/releases/tag/v2.1.0 (use https://github.com/willox/auxtools/releases/tag/v2.2.0))

There are plenty of compiler features missing on the debug server's end, but it is definitely more than usable so I want to get it published. I plan on going a lot further this all of this, maybe we'll even have hot loading one day.

Noticeable differences from actual BYOND are:

1. It only compiles expressions! This means no for loops, no if statements, etc.
2. It lacks all static typing - the compiler has no access to type definitions and will treat all . accesses as : accesses and ignore the rules of const.
3. There are no implicit uses of src. This comes from the fact that there is no static typing, so to access a field on src you have to explicitly use src.xyz syntax.
4. Strings are lame. There is no interpolation support and the escape sequences are super limited too.
5. Some built-in procs aren't supported, but most are. They'll gracefully error if you try to use them.
6. No pre-processor.

For other limitations, just view the error list: https://github.com/willox/dmasm/blob/9ba328ef8c4e45c64072198e72c412cd9f685609/src/compiler.rs#L45-L76

tl;dr: relatively well-working debug console eval, watch eval, and conditional breakpoints

[willox]

I forgot to mention that this would require another proc to be added to code-bases.

/proc/auxtools_expr_stub()
	return

The whole thing works by replacing this proc's bytecode at runtime and then calling it. If you are missing the proc, it just won't work. No crashes or anything.

[willox]

I've released another debug server update since opening this PR, so I'd suggest shipping 2.1.0 instead of 2.0.0.

https://github.com/willox/auxtools/releases/tag/v2.1.0

[willox]

another one: https://github.com/willox/auxtools/releases/tag/v2.2.0

[SpaceManiac]

Looked good enough in testing to merge, but here's a few bug reports:

1. Seems like it's not possible to call verbs - they come out undefined instead
2. If eval hits a breakpoint, there's a None.unwrap() on debug_server/src/server.rs:1203
3. "runtime occurred when executing" message has an extra newline at the end