Add functions for each Value case (#9736)

# Description
This PR ensures functions exist to extract and create each and every
`Value` case. It also renames `Value::boolean` to `Value::bool` to match
`Value::test_bool`, `Value::as_bool`, and `Value::Bool`. Similarly,
`Value::as_integer` was renamed to `Value::as_int` to be consistent with
`Value::int`, `Value::test_int`, and `Value::Int`. These two renames can
be undone if necessary.

# User-Facing Changes
No user facing changes, but two public functions were renamed which may
affect downstream dependents.

crates/nu-command/src/strings/str_/contains.rs

@@ -164,7 +164,7 @@ fn action(
     head: Span,
 ) -> Value {
     match input {
-        Value::String { val, .. } => Value::boolean(
+        Value::String { val, .. } => Value::bool(
             match case_insensitive {
                 true => {
                     if *not_contain {

crates/nu-command/src/strings/str_/ends_with.rs

@@ -94,7 +94,7 @@ fn action(input: &Value, args: &Arguments, head: Span) -> Value {
             } else {
                 s.ends_with(&args.substring)
             };
-            Value::boolean(ends_with, head)
+            Value::bool(ends_with, head)
         }
         Value::Error { .. } => input.clone(),
         _ => Value::Error {

crates/nu-command/src/strings/str_/starts_with.rs

@@ -110,7 +110,7 @@ fn action(
             } else {
                 s.starts_with(substring)
             };
-            Value::boolean(starts_with, head)
+            Value::bool(starts_with, head)
         }
         Value::Error { .. } => input.clone(),
         _ => Value::Error {