[clang] Do less advertising for unresolved issues in `cxx_dr_status.html` (#78836)

This patch places additional requirement on tests for open issues to
specify what do they test, and reduce their advertising on
`cxx_dr_status.html`.

Tests for open issues have to either provide date of the proposed
resolution they test, or a paper number that attempts to resolve the
issue. Examples from this patch: `// dr1223: 17 drafting 2023-05-12`,
`// dr2049: 18 drafting P2308R1`, `// dr2335: no drafting 2018-06`.

Tests for open issues are no longer advertised in `cxx_dr_status.html`
as tests for resolved issues. Instead, they are specified as `Not
Resolved*` (note the asterisk). Such statuses have a tooltip with the
following kind of text:
`Clang 17 implements 2023-05-12 resolution`
`Clang does not implement 2018-06-04 resolution` 
`Clang 18 implements P2308R1 resolution`
I admit that the wording is a bit crude, but I tried to minimize amount
of boilerplate in the `make_cxx_dr_status`. Hopefully, th...