Encode JSON_VIEW_NO_SIMD and JSON_VIEW_USE_SSSE3 in the ABI namespace

Both macros select between definitions of the same inline functions, so
translation units that disagree on them violated the ODR. Like the other
ABI-affecting macros, they now add a tag to the inline namespace (_vns and
_vssse3), and the docs replace the "Define consistently" warning with the
usual ABI compatibility note. From gregmarr's review of #5628.

nlohmann_json.natvis covers twice as many tags now, so it lists four times
as many namespaces (14.7 MB instead of 3.4 MB).

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

docs/mkdocs/docs/api/macros/json_view_use_ssse3.md

@@ -17,12 +17,12 @@ Define the macro only together with a compiler option that enables SSSE3 (e.g. `
 has it), and only for programs that run on such CPUs. It saves the check of the CPU, which costs little. The same
 input is accepted or rejected either way; only the speed of non-ASCII text differs.
 
-!!! warning "Define consistently"
+!!! note "ABI compatibility"
 
-    The macro selects between two definitions of the same inline functions. It must therefore be defined identically,
-    with the same compiler options, for **every** translation unit that includes `<nlohmann/json_view.hpp>`; mixing
-    translation units that define it with ones that do not is an ODR violation. Prefer a compile definition on the
-    target.
+    The macro selects between two definitions of the same inline functions. Whether it is defined is encoded in the
+    [namespace](../../features/namespace.md) (tag `_vssse3`, on every architecture), resulting in distinct symbol
+    names. Translation units compiled with and without it can therefore be linked into the same program without One
+    Definition Rule (ODR) violations, but they cannot exchange instances of library types.
 
 ## Default definition