Improved spans for generated code and error messages

[jamie-osec]

Anchor generates a lot of code in the #[program] macro. When the user code contains errors, the resulting error messages are unhelpful:

  --> programs/test-instruction-validation/src/lib.rs:7:1
   |
7  | #[program]
   | ^^^^^^^^^^ expected `u8` here based on `#[instruction(...)]` attribute, found `u64`

As they point to the program macro instead of the relevant code.
This can be improved by replacing uses of quote!{} with quote_spanned!, to ensure the generated code corresponds to the correct code location.