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>

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

docs/mkdocs/docs/features/assertions.md

@@ -7,7 +7,9 @@ detect bugs in client code.
 ## Switch off runtime assertions
 
 Runtime assertions can be switched off by defining the preprocessor macro `NDEBUG` (see the
-[documentation of assert](https://en.cppreference.com/w/cpp/error/assert)) which is the default for release builds.
+[documentation of assert](https://en.cppreference.com/w/cpp/error/assert)) which is the default for release builds. Without `NDEBUG`, the assertions are compiled in and contain the name of the source
+file (`__FILE__`); see [notes for builds and distribution](../integration/index.md#notes-for-builds-and-distribution)
+if that path must not end up in your binaries.
 
 ## Change assertion behavior