Deprecate date to-record and date to-table (#14319)

# Description

Implements #11234 based on the comments there:

* (Previously implemented): `into record` handles nanoseconds (as well
as milliseconds and microseconds, which the deprecated commands didn't
support).
* Added deprecation warning to `date to-record` and `date to-table`
* Added new example for `into record` showing the conversion to a table
* Changed `std/dt` to use `into record`
* Added "Deprecated" category back to nu-protocol::Signature
* Assigned the deprecated commands to the Deprecated category so be
categorized properly in the online Doc.

# User-Facing Changes

Deprecated command warning

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Searched doc for existing uses of `date to-record` and `date to-table`:

* For primary English-language docs, there are no uses other than in the
auto-generated command help, which will be updated based on this PR
* Other language translations appear to have an old use in several
places and will need to be updated to match the English-language doc.

crates/nu-std/std/dt/mod.nu

@@ -120,8 +120,8 @@ export def datetime-diff [
             }
         }
     }
-    let from_expanded = ($later | date to-timezone utc | date to-record)
-    let to_expanded = ($earlier | date to-timezone utc | date to-record)
+    let from_expanded = ($later | date to-timezone utc | into record)
+    let to_expanded = ($earlier | date to-timezone utc | into record)
 
     mut result = { year: ($from_expanded.year - $to_expanded.year), month: ($from_expanded.month - $to_expanded.month), day:0, hour:0, minute:0, second:0, millisecond:0, microsecond:0, nanosecond:0}