More documentation updates for 3.11.0 (#3553)

* mkdocs: add string_view examples

* mkdocs: reference underlying operators

* mkdocs: add operator<=> examples

* mkdocs: fix style check issues

* mkdocs: tweak BJData page

* mkdocs: add CMake option hints to macros

* mkdocs: fix JSON_DISABLE_ENUM_SERIALIZATION definition

* mkdocs: fix link to unit-udt.cpp

* mkdocs: fix "Arbitrary Type Conversions" title

* mkdocs: link to api/macros/*.md instead of features/macros.md

* mkdocs: document JSON_DisableEnumSerialization CMake option

* mkdocs: encode required C++ standard in example files

* docset: detect gsed/sed

* docset: update index

* docset: fix CSS patching

* docset: add list_missing_pages make target

* docset: add list_removed_paths make target

* docset: replace page titles with name from index

* docset: add install target for Zeal docset browser

* Use GCC_TOOL in ci_test_documentation target

docs/mkdocs/docs/api/basic_json/operator_spaceship.md

@@ -55,6 +55,36 @@ Linear.
         2. Comparing a `NaN` with another `NaN`.
         3. Comparing a `NaN` and any other number.
 
+## Examples
+
+??? example "Example: (1) comparing JSON values"
+
+    The example demonstrates comparing several JSON values.
+    
+    ```cpp
+    --8<-- "examples/operator_spaceship__const_reference.c++20.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator_spaceship__const_reference.c++20.output"
+    ```
+
+??? example "Example: (2) comparing JSON values and scalars"
+
+    The example demonstrates comparing several JSON values and scalars.
+    
+    ```cpp
+    --8<-- "examples/operator_spaceship__scalartype.c++20.cpp"
+    ```
+    
+    Output:
+    
+    ```json
+    --8<-- "examples/operator_spaceship__scalartype.c++20.output"
+    ```
+
 ## See also
 
 - [**operator==**](operator_eq.md) - comparison: equal