Build or triage every code sample; import/export fixes

[KubaO]

Code samples

• 1,116 of the 1,168 code samples now build, up from 818, in about 110 seconds.
• Each of the other 52 is marked inert= with its reason, so no sample is undecided.
• Fixed samples that were wrong rather than incomplete, among them Generics, the Arrays tutorial and Screen.
• Dim x As New Foo(args) is a syntax error, so those samples now use Set x = New Foo(args).
• Samples using a package's private types or enums import it with an asterisk, and each page explains how.
• The CustomControls tutorials use the serializer's current names and read designer values through GetSerializer.
• The Painting tutorial's samples build, with Canvas members under their real names.
• Samples declare their locals, put loose statements in a Sub, and write elisions as ' ....
• The last excerpts build, showing what the reader writes and hiding what they bring from elsewhere.
• Interface and Err.Source no longer show code that a compiler bug refuses.

Import and export

• impexp export now converts LF to CRLF in .twin, .bas and .cls files, as the compiler's import does.
• Every other file is still stored byte-for-byte, so resources are never altered.
• The Import/Export Tool page describes this conversion for both tools.
• It also documents that the compiler's import fails, with exit code 999, on any project that embeds a package.
• The standalone scripts pack such a project correctly, and the page's comparison table says so.
• The page no longer claims the compiler's exit code is always zero.

Tooling

• check_examples gains inert=<reason>, to record why a fence is not a program.
• resource= stages a file the compiler reads, so [PopulateFrom] is checked against its page's JSON.
• concat_group= joins one construct shown across several fences into a single unit.
• --report groups a saved survey by diagnostic, section, undeclared symbol and page.
• A diagnostic inside a package's own source is traced to the sample that caused it, which used to pass.
• New templates import CustomControls, WinNativeCommonCtls and CEF with an asterisk; implicit turns Option Explicit off.
• The stage set gains 61 declarations for the controls and objects the samples assume.
• The classifier reads top-level Implements and Inherits as class code-behind, and . . . as an elision.
• A sample may bring its own Sub Main; the rule against it was never true.
• check_examples explains the EPERM that a dead run's leftover IDEs cause.
• tbrun, check_examples and the attribute census test the compiler's output for ... DONE, not its exit code.
• tbrun no longer reports a packing failure as compile errors, and the census no longer caches a failed export.

Bugs queued in BUGS-TO-REPORT.md

• Public members are typed with private components, so a default project cannot use them.
• Err.Raise rejects HelpContext:=, although its other named arguments work.
• A class cannot implement an interface member marked [PreserveSig].
• The compiler's import stops with exit code 999 on a tree that embeds a package.
• export and import stop at the 260-character path limit, and still exit 0.

Notes

• Authoring.md explains the new markers, finishing a sample that is one line short, and what to hide.
• Authoring.md adds a rule: document the product as it is, not as it was.
• WIP.ExamplesBuild.md records the marking, editorial and excerpt passes.
• The attribute census is re-measured at 661 files and 9,701 sites.