Expose "to html" command (#14536)

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# Description
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In this PR I exposed the struct `ToHtml` that comes from `nu-cmd-extra`.
I know this command isn't in a best state and should be changed in some
way in the future but having the struct exposed makes transforming data
to html way more simple for external tools as the `PipelineData` can
easily be placed in the `ToHtml::run` method.

# User-Facing Changes
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None.

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I did `fmt` and `check` but not `test`, shouldn't break any tests
regardless.

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For the demo page or my jupyter kernel would this make my life easiert.

crates/nu-cmd-extra/src/extra/formats/mod.rs

@@ -2,4 +2,4 @@ mod from;
 mod to;
 
 pub(crate) use from::url::FromUrl;
-pub(crate) use to::html::ToHtml;
+pub use to::html::ToHtml;

crates/nu-cmd-extra/src/extra/mod.rs

@@ -9,6 +9,7 @@ mod strings;
 pub use bits::{
     Bits, BitsAnd, BitsInto, BitsNot, BitsOr, BitsRol, BitsRor, BitsShl, BitsShr, BitsXor,
 };
+pub use formats::ToHtml;
 pub use math::{MathArcCos, MathArcCosH, MathArcSin, MathArcSinH, MathArcTan, MathArcTanH};
 pub use math::{MathCos, MathCosH, MathSin, MathSinH, MathTan, MathTanH};
 pub use math::{MathExp, MathLn};
@@ -54,7 +55,8 @@ pub fn add_extra_command_context(mut engine_state: EngineState) -> EngineState {
             strings::str_::case::StrTitleCase
         );
 
-        bind_command!(formats::ToHtml, formats::FromUrl);
+        bind_command!(ToHtml, formats::FromUrl);
+
         // Bits
         bind_command! {
             Bits,