Address the review of erase() in editable json documents

From gregmarr's review of #5630:

- invalid_iterator.202 is thrown by overloads 1 and 2 only; the page said
  "every overload" and then excluded 3 in parentheses.
- The note on links says what moves (the links after the removed element,
  as insert() moves them the other way) and that every iterator over the
  container is invalidated, not only those after the removed element.
- edit.hpp compares keys with document_data::key_equals().

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json_document/erase.md

@@ -69,10 +69,10 @@ has `erase`; calling it on a read-only `basic_json_document` fails to compile (`
    [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) (an empty token); otherwise (an
    object, or a primitive value the pointer's parent resolves to) throws what 1. throws.
 
-Every overload also throws [`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202) ("view
-does not belong to this document") if `object`/`array` is a [discarded](../basic_json_view/is_discarded.md) view or a
-view of a *different* document (overloads 1-2 only; overload 3 always starts from this document's own
-[`root()`](root.md)).
+Overloads 1. and 2. also throw [`invalid_iterator.202`](../../home/exceptions.md#jsonexceptioninvalid_iterator202)
+("view does not belong to this document") if `object`/`array` is a [discarded](../basic_json_view/is_discarded.md)
+view or a view of a *different* document. Overload 3. takes no view: it always starts from this document's own
+[`root()`](root.md).
 
 ## Complexity
 
@@ -92,9 +92,10 @@ view of a *different* document (overloads 1-2 only; overload 3 always starts fro
 
 Like [`set`](set.md) and [`push_back`](push_back.md), `erase` never moves an element's *value*: a view still
 referring to a removed member or element keeps showing what it last held (see [Edits](index.md#edits)) -- it just no
-longer appears when `array`/`object` is read, dumped, or iterated. Removing an element of `array` (2.) does shift the
-*links* to the elements after it, the same way `insert`, `set`, or `push_back` on the same array would; any iterator
-already taken over `array`/`object` is invalidated by an erase, since it was walking the old layout.
+longer appears when `array`/`object` is read, dumped, or iterated. What does change is the container's sequence of
+*links* to its elements: removing an element of `array` (2.) shifts the links to the elements after it by one, as
+[`insert`](insert.md) does in the other direction. *Every* iterator already taken over `array`/`object` is invalidated
+by an erase, not only those at or after the removed element, since the container may now use a different sequence.
 
 ## Examples
 

include/nlohmann/detail/view/edit.hpp

@@ -12,7 +12,7 @@
 #include <cmath> // isinf, isnan
 #include <cstddef> // size_t
 #include <cstdint> // int64_t, uint8_t, uint32_t, uint64_t
-#include <cstring> // memcmp, memmove
+#include <cstring> // memmove
 #include <limits> // numeric_limits
 #include <string> // string, to_string
 #include <type_traits> // decay, enable_if, integral_constant, is_arithmetic, is_convertible, is_floating_point, is_same, is_signed
@@ -313,7 +313,7 @@ class editor
 
     bool key_equals(const node& k, string_view_t key) const noexcept
     {
-        return k.len == key.size() && (key.size() == 0 || std::memcmp(m_doc.str(k), key.data(), key.size()) == 0);
+        return m_doc.key_equals(k, key.data(), key.size());
     }
 
     /// remove the members with this key (all, or all but the first) from an object