checker: cleanup and move test files to tests directory (#22870)

Author: yuyi98

vlib/v/checker/or_block_assert_err.out

@@ -0,0 +1,12 @@
+vlib/v/checker/tests/or_block_assert_err.vv:10:22: error: last statement in the `or {}` block should be an expression of type `int` or exit parent scope
+    8 | 
+    9 | f() or { assert true }
+   10 | a := f() or { assert true }
+      |                      ~~~~~~
+   11 | dump(a)
+   12 | g(f() or { assert true })
+vlib/v/checker/tests/or_block_assert_err.vv:12:19: error: last statement in the `or {}` block should be an expression of type `int` or exit parent scope
+   10 | a := f() or { assert true }
+   11 | dump(a)
+   12 | g(f() or { assert true })
+      |                   ~~~~~~