Consolidate on `loaderData` name instead of `data` for types

[brophdawg11]

Discussed in #13934

^{Originally posted by rossipedia July 4, 2025}
There's a bit of an inconsistency in which types use loaderData and which use just data:

• CreateMetaArgs uses data for the loader data
• CreateHydrateFallbackProps uses loaderData and actionData
• CreateComponentProps uses loaderData and actionData
• Match uses data to mean "loader data"
• MetaMatch also uses data to mean "loader data"

Inconsistent names are harder to reason about, and harder to work with when code-modding larger codebases. There's a bit of extra cognitive overhead too ("Data? Is this loader data? Action data? wait... which one even makes sense in this context? hmmm")

I propose all data properties be explicitly named either loaderData or actionData to reflect what their actual data represents.

This could be done incrementally (as suggested by @MichaelDeBoey on Discord):

• Introduce loaderData and actionData where needed as a duplicate property for the existing ambiguous data
• Mark data as @deprecated
• Remove data in a future major version

[brophdawg11]

This is available in 0.0.0-experimental-909c02f10 for alpha testing