[Slim] Encode path to support non-latin characters

Created by: ybelenko

PR checklist

• Read the contribution guidelines.
• Ran the shell script under ./bin/ to update Petstore sample so that CIs can verify the change. (For instance, only need to run ./bin/{LANG}-petstore.sh and ./bin/security/{LANG}-petstore.sh if updating the {LANG} (e.g. php, ruby, python, etc) code generator or {LANG} client's mustache templates). Windows batch files can be found in .\bin\windows\.
• Filed the PR against the correct branch: master, 3.4.x, 4.0.x. Default: master.
• Copied the technical committee to review the pull request if your PR is targeting a particular programming language.

Description of the PR

Closes: #766 (closed) This PR should be reviewed carefully, because I didn't find a way to fix it without DefaultGenerator modification.

As it turns out {{basePathWithoutHost}} construction doesn't solve issue when path contains non-latin characters. For instance, Slim router cannot find related API controller when path looks like /статьи/авторы, because escaped mustache variable output is /статьи/авторы without any difference, while HTTP clients and web browsers encodes non-latin characters by default. When I use this link in Chrome I see in server logs that url has been automatically encoded into /%D1%81%D1%82%D0%B0%D1%82%D1%8C%D0%B8/%D0%B0%D0%B2%D1%82%D0%BE%D1%80%D1%8B. The same behaviour with Insomnia app. With new method encodePath Slim router works as expected.

I've also added few tests to check encodePath method output of PhpSlimServerCodegen.

cc @jebentier @dkarlovi @mandrean @jfastnacht @ackintosh @renepardon