Fix contradictions between the documentation, the README, and the library (#5825)

- Discarded values: the legacy macro only changes <= and >=; != is true by default
- Out-of-range numbers are rejected while parsing, not stored as NaN
- merge_diff round trip: point to the ordered_json caveat
- ensure_ascii example shows the escaped output
- out_of_range.405 is thrown for "remove"/"move" on the root, not "add"
- CBOR stores binary subtypes as tags
- Integer/float comparison uses exact values, not conversion
- diff, flatten, and the binary writers are depth-bounded
- FAQ: max_digits10 for serialization, trailing commas are supported
- out_of_range.407 is still thrown by to_bon8
- FetchContent_MakeAvailable needs CMake 3.14
- json_fwd.hpp contents, operator< link, RFC 7396 for merge patch
- README: dump() wording, merge_diff, MSYS2/build2, patch comment typos,
  operator[] link, embedded CMake example aligned with the docs

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

docs/mkdocs/docs/api/basic_json/operator_eq.md

@@ -20,7 +20,8 @@ bool operator==(ScalarType rhs) const noexcept(/* see below */); // (2)
 1. Compares two JSON values for equality according to the following rules:
     - Two JSON values are equal if (1) neither value is discarded, and (2) they are of the same type and their stored
       values are the same according to their respective `operator==`.
-    - Integer and floating-point numbers are automatically converted before comparison.
+    - Integer and floating-point numbers are compared by their exact values, without converting the integer to
+      floating-point. For instance, `9007199254740993` and `9007199254740992.0` are not equal.
 
 2. Compares a JSON value and a scalar or a scalar and a JSON value for equality by converting the
    scalar to a JSON value and comparing both JSON values according to 1.