[analyzer] Unbreak [[clang::suppress]] on checkers without decl-with-issue. (#79398)

There are currently a few checkers that don't fill in the bug report's
"decl-with-issue" field (typically a function in which the bug is
found).

The new attribute `[[clang::suppress]]` uses decl-with-issue to reduce
the size of the suppression source range map so that it didn't need to
do that for the entire translation unit.

I'm already seeing a few problems with this approach so I'll probably
redesign it in some point as it looks like a premature optimization. Not
only checkers shouldn't be required to pass decl-with-issue (consider
clang-tidy checkers that never had such notion), but also it's not
necessarily uniquely determined (consider leak suppressions at
allocation site).

For now I'm adding a simple stop-gap solution that falls back to
building the suppression map for the entire TU whenever decl-with-issue
isn't specified. Which won't happen in the default setup because luckily
all default checkers do provide decl-with-issue.

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Co-authored-by: Balazs Benics <benicsbalazs@gmail.com>