[BUG] `amber check` should check pub functions even if they are not called

[lens0021]

To Reproduce

git switch --detach 3d0b2a2aa5c72606850a5d00159097067ce36c68` # a commit on `staging`
cargo run -- check src/std/env.ab

Expected behavior

 WARN  Invalid escape sequence '\x'
at src/std/env.ab:84:43

83| pub fun input_confirm(prompt: Text, default_yes: Bool = false): Bool {
84|     let choice_default = default_yes then " [\x1b[1mY/\x1b[0mn]" else " [y/\x1b[1mN\x1b[0m]"
85|     trust {
Only these escape sequences are supported: \n, \t, \r, \0, \{, \$, \', \", \\
 WARN  Invalid escape sequence '\x'
at src/std/env.ab:84:43

...

Actual behavior Nothing printed with exit code 0.

Additional context I have a plan to add a GitHub Actions workflow that executes amber check for all amber files.

[Ph0enixKM]

This is something that is blocked by #770