Provide Error Message on Settings Configuration

[bscan]

When a user enters a settings.perlPath, the Navigator should validate that the file exists and is a valid perl executable. If not, pop-up a nice error message to the user with the path attempted and suggested fix. See the following for references:

https://github.com/rust-lang/rust-analyzer/blob/7d1015b8d177a02dff03d2c70bc74e5d4ed34335/editors/code/src/main.ts#L19-L26

https://github.com/microsoft/vscode-languageserver-node/commit/980bf45add3062b3f14184394103d251ef42bae1

Ensure this is designed in a way to support other error messages. For example, if Perl::Critic or Perl::Tidy are not installed, or if they throw errors such as invalid critic/tidy configuration settings, or if they fail for any reason (e.g. encodings).