Make hook execution stream instead of collecting (#7440)

Closes #7431. In a nutshell:
- `run_hook_block()` in repl.rs was collecting all input into a `Value`
instead of handling streaming input properly
- this was a problem because now we have a default `display_output` hook
that _everything_ gets piped to
- this PR fixes the problem by tweaking `run_hook_block()` to return a
`PipelineData` instead of a `Value`

After this change, individual pages are rendered as they finish. This is
a little easier to see if I tweak `STREAM_PAGE_SIZE` in table.rs to 10:

![image](https://user-images.githubusercontent.com/26268125/206935370-412b2ee9-9401-4222-bc93-5bd5a9adc13b.png)

## Future work

This does _not_ fix https://github.com/nushell/nushell/issues/7342.

crates/nu-cli/src/repl.rs

@@ -709,6 +709,13 @@ pub fn eval_hook(
 ) -> Result<PipelineData, ShellError> {
     let value_span = value.span()?;
 
+    // Hooks can optionally be a record in this form:
+    // {
+    //     condition: {|before, after| ... }  # block that evaluates to true/false
+    //     code: # block or a string
+    // }
+    // The condition block will be run to check whether the main hook (in `code`) should be run.
+    // If it returns true (the default if a condition block is not specified), the hook should be run.
     let condition_path = PathMember::String {
         val: "condition".to_string(),
         span: value_span,
@@ -748,16 +755,19 @@ pub fn eval_hook(
                                 arguments.clone(),
                                 block_span,
                             ) {
-                                Ok(value) => match value {
-                                    Value::Bool { val, .. } => val,
-                                    other => {
+                                Ok(pipeline_data) => {
+                                    if let PipelineData::Value(Value::Bool { val, .. }, ..) =
+                                        pipeline_data
+                                    {
+                                        val
+                                    } else {
                                         return Err(ShellError::UnsupportedConfigValue(
                                             "boolean output".to_string(),
-                                            format!("{}", other.get_type()),
-                                            other.span()?,
+                                            "other PipelineData variant".to_string(),
+                                            block_span,
                                         ));
                                     }
-                                },
+                                }
                                 Err(err) => {
                                     return Err(err);
                                 }
@@ -880,34 +890,28 @@ pub fn eval_hook(
             span: block_span,
             ..
         } => {
-            output = PipelineData::Value(
-                run_hook_block(
+            output = run_hook_block(
                 engine_state,
                 stack,
                 *block_id,
                 input,
                 arguments,
                 *block_span,
-                )?,
-                None,
-            );
+            )?;
         }
         Value::Closure {
             val: block_id,
             span: block_span,
             ..
         } => {
-            output = PipelineData::Value(
-                run_hook_block(
+            output = run_hook_block(
                 engine_state,
                 stack,
                 *block_id,
                 input,
                 arguments,
                 *block_span,
-                )?,
-                None,
-            );
+            )?;
         }
         other => {
             return Err(ShellError::UnsupportedConfigValue(
@@ -931,7 +935,7 @@ pub fn run_hook_block(
     optional_input: Option<PipelineData>,
     arguments: Vec<(String, Value)>,
     span: Span,
-) -> Result<Value, ShellError> {
+) -> Result<PipelineData, ShellError> {
     let block = engine_state.get_block(block_id);
 
     let input = optional_input.unwrap_or_else(PipelineData::empty);
@@ -955,9 +959,11 @@ pub fn run_hook_block(
 
     match eval_block_with_early_return(engine_state, &mut callee_stack, block, input, false, false)
     {
-        Ok(pipeline_data) => match pipeline_data.into_value(span) {
-            Value::Error { error } => Err(error),
-            val => {
+        Ok(pipeline_data) => {
+            if let PipelineData::Value(Value::Error { error }, _) = pipeline_data {
+                return Err(error);
+            }
+
             // If all went fine, preserve the environment of the called block
             let caller_env_vars = stack.get_env_var_names(engine_state);
 
@@ -973,10 +979,8 @@ pub fn run_hook_block(
             for (var, value) in callee_stack.get_stack_env_vars() {
                 stack.add_env_var(var, value);
             }
-
-                Ok(val)
+            Ok(pipeline_data)
         }
-        },
         Err(err) => Err(err),
     }
 }