Better syntax error reporting

[ZedThree]

The tree-sitter error reporting is rather lacklustre, and we may currently flag an entire file as being a syntax error in some circumstances. Unfortunately some errors cascade and a single error can be reported in multiple subsequent places. For example, this file has 11 errors, including the whole file, because there are two variables containing $, which is non-standard: https://github.com/bmad-sim/bmad-ecosystem/blob/028ad6228336eae46adc5df4e781b33384a78313/util_programs/wake_plot/wake_plot.f90#L135-L142

We can distinguish between node.is_error(), .has_error(), .is_missing(), and .is_extra(). This might let us narrow things down.