Add missing 'form' attribute for <mo> MathML element

[lnay]

Although this attribute seems to be missing in the attribute table on Mozilla Docs for that tag ,
it does appear in the compatibility table lower down.
This attribute is also frequently used by temml, a common generator for MathML content.

WARNING: I haven't set up a dev or test env, and hoping this this can be picked up by somebody else as a quick fix if what I did was incorrect.

Mainly doing this to raise awareness of the issue.

[lnay]

I ran cargo make check && cargo make test && cargo make check-examples,
failing with identical errors as when I run it on the current head of the leptos_0.7 branch:

error[E0412]: cannot find type `SerdeLite` in this scope
   --> leptos_server/src/resource.rs:161:24
    |
161 | impl<T> ArcResource<T, SerdeLite>
    |                        ^^^^^^^^^ not found in this scope
    |
help: you might be missing a type parameter
    |
161 | impl<T, SerdeLite> ArcResource<T, SerdeLite>
    |       +++++++++++

error[E0412]: cannot find type `SerdeLite` in this scope
   --> leptos_server/src/resource.rs:163:33
    |
163 |     T: Debug + SerializableData<SerdeLite>,
    |                                 ^^^^^^^^^ not found in this scope
    |
help: you might be missing a type parameter
    |
161 | impl<T, SerdeLite> ArcResource<T, SerdeLite>
    |       +++++++++++

error[E0277]: the trait bound `T: SerializableData<_>` is not satisfied
   --> leptos_server/src/resource.rs:176:9
    |
176 |         ArcResource::new_with_encoding(source, fetcher)
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `SerializableData<_>` is not implemented for `T`
    |
    = help: the following other types implement trait `SerializableData<Ser>`:
              <T as SerializableData<SerdeJson>>
              <T as SerializableData<rkyv::Rkyv>>
              <T as SerializableData<serializers::Str>>
note: required by a bound in `ArcResource::<T, Ser>::new_with_encoding`
   --> leptos_server/src/resource.rs:183:16
    |
183 |     T: Debug + SerializableData<Ser>,
    |                ^^^^^^^^^^^^^^^^^^^^^ required by this bound in `ArcResource::<T, Ser>::new_with_encoding`
...
187 |     pub fn new_with_encoding<S, Fut>(
    |            ----------------- required by a bound in this associated function

[gbj]

Thank you thank you! CI is in a broken state at present for the core packages and that's fine, I appreciate the diligence and the PR.

[gbj]

Also super glad to see someone using MathML, and glad we have built-in support for it :-)

[lnay]

Thanks, I've experienced quirks with MathML in other frameworks and glad to see its support in leptos 0.7.

Leptos has been a really good fit so far for packaging a mathematical Rust crate into both a Python/SageMath library as well as a WebApp for exposure!