[fine] Many test improvements, error improvements

- Check for more error conditions
- Move to more definitive error assertions
- Simpler error messages in some cases
- Test more conditions more thoroughly, revisit old tests

fine/tests/expression/errors/if_requires_else.fine

@@ -1,2 +1,4 @@
 if (if false { true }) { 32 } else { 23 }
-// @type-error: 4 the type of the `then` branch (bool) must match the type of the `else` branch (())
+
+// @expect-errors:
+// | 1:4: the type of the 'then' branch ('bool') must match the type of the 'else' branch ('()')