Port str case commands (#287)

* Port camel case and kebab case

* Port pascal case

* Port snake case and screaming snake case

* Cleanup before PR

* Add back cell path support for str case commands

* Add cell path tests for str case command

* Revert "Add cell path tests for str case command"

This reverts commit a0906318d95fd2b5e4f8ca42f547a7e4c5db381a.

* Add cell path test cases for str case command

* Move cell path tests from tests.rs to Examples in each of the command's file

Co-authored-by: Stefan Stanciulescu <contact@stefanstanciulescu.com>

crates/nu-command/src/default_context.rs

@@ -25,6 +25,7 @@ pub fn create_default_context() -> EngineState {
             Alias,
             Benchmark,
             BuildString,
+            CamelCase,
             Cd,
             Cp,
             Date,
@@ -47,6 +48,7 @@ pub fn create_default_context() -> EngineState {
             FromJson,
             Get,
             Griddle,
+            KebabCase,
             Help,
             Hide,
             If,
@@ -80,12 +82,15 @@ pub fn create_default_context() -> EngineState {
             Mkdir,
             Module,
             Mv,
+            PascalCase,
             ParEach,
             Ps,
             Range,
             Rm,
             Select,
             Size,
+            ScreamingSnakeCase,
+            SnakeCase,
             Split,
             SplitChars,
             SplitColumn,