Docs: fill documentation gaps found in user questions (#5907)

* Docs: fill documentation gaps found in user questions

Add pages on class-hierarchy/smart-pointer/variant/chrono recipes, working
without exceptions, and large, streamed and partial input. Extend the FAQ
(23 entries, Known bugs first), parse error documentation (empty-input
checklist, line/column, diagnostic positions), element access, conversions,
creating values, ADL troubleshooting, memory, and build/distribution notes.
Add 14 examples with generated output. Correct the statement that parse errors
cannot be recovered from with -fno-exceptions.

The topics come from recurring questions on Stack Overflow, Reddit, Hacker
News, YouTube, and the project's GitHub discussions and issues.

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

* docs: declare range-for lists in variables to keep astyle quiet

astyle reformats a braced init list placed directly in a range-for
header; declare the list first so check_amalgamation passes.

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

---------

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

docs/mkdocs/mkdocs.yml

@@ -106,6 +106,7 @@ nav:
   - Features:
       - features/index.md
       - features/arbitrary_types.md
+      - features/type_recipes.md
       - Binary Formats:
           - features/binary_formats/index.md
           - features/binary_formats/bjdata.md
@@ -130,11 +131,13 @@ nav:
       - features/modifying_values.md
       - features/modules.md
       - 'nlohmann Namespace': features/namespace.md
+      - features/no_exceptions.md
       - features/object_order.md
       - features/performance.md
       - Parsing:
           - features/parsing/index.md
           - features/parsing/json_lines.md
+          - features/parsing/large_and_partial_input.md
           - features/parsing/parse_exceptions.md
           - features/parsing/parser_callbacks.md
           - features/parsing/sax_interface.md