Allow the same type for number_integer_t and number_unsigned_t (#5815)

* Allow the same type for number_integer_t and number_unsigned_t

basic_json did not compile with NumberUnsignedType == NumberIntegerType
because overloads on both types collided. Such a basic_json now stores
every integer as number_integer: the colliding overloads take a
placeholder type, unsigned C++ integers are converted to number_integer_t,
and value_t::number_unsigned maps to number_integer.

Also fixes two problems this configuration would hit: the unsigned
integer parser accepted values that wrap around to negative numbers, and
dump() overflowed when computing the absolute value of the minimum.

A repeated NumberFloatType gets a static_assert.

Refs #2573

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

* Use json::with_integers_t in the test and the docs

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

* ✅ skip patch test on GCC 5 to avoid internal compiler error

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

* Fix CI: name the unsigned overload type through template parameters

basic_json used number_unsigned_overload_t<basic_json> while the class was
still incomplete. MSVC rejected it as a recursive alias declaration and GCC
4.9, 5 and 7 crashed with an internal compiler error. basic_json now uses
number_unsigned_overload_type<NumberIntegerType, NumberUnsignedType>, which
also makes the GCC 5 workaround in the patch test unnecessary.

Infer reported a null dereference for the number_unsigned case in
from_json, which cannot happen for a basic_json whose number_unsigned_t is
number_integer_t; assert it.

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

* Address review: conjunction/negation trait, astyle-friendly alias, docs table order

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

---------

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

docs/mkdocs/docs/api/basic_json/is_number_unsigned.md

@@ -6,6 +6,9 @@ constexpr bool is_number_unsigned() const noexcept;
 
 This function returns `#!cpp true` if and only if the JSON value is an unsigned integer number. This excludes
 floating-point and signed integer values.
+
+If [`number_unsigned_t`](number_unsigned_t.md) is the same type as [`number_integer_t`](number_integer_t.md), every
+integer is stored as `number_integer_t`, and this function always returns `#!cpp false`.
     
 ## Return value
 

docs/mkdocs/docs/api/basic_json/number_unsigned_t.md

@@ -25,7 +25,8 @@ the type to use.
 `NumberUnsignedType`
 :   the type to store unsigned integers. It must be an **unsigned integral** type (`#!cpp std::is_integral`) with a
     `#!cpp std::numeric_limits` specialization, and it must be able to represent the absolute value of every
-    [`number_integer_t`](number_integer_t.md) value. See
+    [`number_integer_t`](number_integer_t.md) value. Alternatively, it can be the same type as
+    [`number_integer_t`](number_integer_t.md); then every integer is stored as `number_integer_t`. See
     [Template Parameter Requirements](../../features/types/template_parameters.md#numberintegertype-and-numberunsignedtype).
 
 ## Notes
@@ -89,3 +90,4 @@ Integer number values are stored directly inside a `basic_json` type.
 ## Version history
 
 - Added in version 2.0.0.
+- Can be the same type as `number_integer_t` since version 3.13.0.