In a per-component installation the generated installation scripts
are invoked once for each component.
Per default custom installation script code added by install(CODE|SCRIPT)
only runs for one specific component in this context.
The new ALL_COMPONENTS option allows custom script code to be run once
for each component being installed.
INTERFACE libraries with SOURCES now appear in the generated
buildsystem, so include them in the codemodel output too.
We do not need to bump the `codemodel-v2` object kind minor
version because that was already done in post-3.18 development
by commit 7d6861f367 (fileapi: Extend codemodel targets with
language standard, 2020-06-18).
Fixes: #18608
