Start fixing error outputs

Signed-off-by: Marcel Müller <neikos@neikos.email>

tests/errors/invalid_controls.2-ast.snap

@@ -0,0 +1,32 @@
+---
+source: tests/file_tests.rs
+expression: ast
+info:
+  input: "{{ if }} {{ end }}\n{{ if if }} {{ end }}\n{{ if if }} {{ for foo in bar }} {{ end }} {{ end }}\n{{ for in bar }} {{ end }}\n{{ for blah bar }} {{ end }}\n{{ else }}"
+  context: {}
+---
+error: Expected an expression after 'if'
+  ╭▸ 
+1 │ {{ if }} {{ end }}
+  │    ━━
+  ╰╴
+error: Expected an expression after 'if'
+  ╭▸ 
+2 │ {{ if if }} {{ end }}
+  ╰╴      ━━
+error: Expected an expression after 'if'
+  ╭▸ 
+3 │ {{ if if }} {{ for foo in bar }} {{ end }} {{ end }}
+  ╰╴      ━━
+error: Expected identifier here
+  ╭▸ 
+4 │ {{ for in bar }} {{ end }}
+  ╰╴       ━━━━━━
+error: Missing `in` in `for _ in <expr>`
+  ╭▸ 
+5 │ {{ for blah bar }} {{ end }}
+  ╰╴       ━━━━━━━━
+error: An error occurred while producing an Ast
+  ╭▸ 
+6 │ {{ else }}
+  ╰╴   ━━━━━━━