Add an AST dumper

[krnowak]

I wrote this AST dumper mostly to compare a tree generated by Odin with a tree generated by my odin tree sitter parser. But I guess it could be useful not only for me, so I'm proposing it here.

This adds two new options to the build command - -dump-ast and -dump-ast-opts, both are taking parameters. -dump-ast takes parameters specifying which packages and files should have their ASTs dumped, whereas -dump-ast-opts modify the dumper behavior. From the help output:

	-dump-ast:<string>
		Dumps AST to files. The passed string can either be '-' or a semicolon-separated list of dump specs.
		Dump spec: <package name>[:<comma-separated list of files>]
		Example dump specs:
			utf8 - dump AST for all the files in the utf8 package
			unicode:doc.odin,fold.odin - dump AST only for doc.odin and fold.odin in unicode package

	-dump-ast-opts:<string>
		Options for -dump-ast. The passed string is a comma-separated list of options.
		Possible options:
			sexp - dump AST in S-expression format
			json - dump AST in JSON format
			xml - dump AST in XML format
			omit-defaults - skip values and attributes with default values (false for booleans, empty strings or empty lists)
			disregard-filetags - ignore build effects of file tags, so this will make the compiler only to parse the files and dump the ast
			no-ids - do not print IDs for dumped AST nodes, useful for less-cluttered diffs

I'm not sure which format would be best here, so just wrote three.

An example invocation I was using:

odin build . -dump-ast:- -dump-ast-opts:sexp,omit-defaults,disregard-filetags

This dumps all the files (even those that should not be built, because the OS does not match) in all the imported packages using an S-expression format, making the output a bit shorter by skipping fields set to default values.

This turned out to be helpful in finding issues with #force_inline, package docs, procedures with diverging results and probably something else too.