Similar to #17807, this adds
locale-independent handling for isspace.

I have to say I don't remember exactly if I manage to reproduce a
problem with this or just looked right to have.

Feedback on the implementation welcome.

Improved version of #17807, using
infrastructure from #17866 to check
`std::stringstream` are not used anymore at compile time.

Original problem I had bumped in duckdb-wasm, where there would be some
yet to be properly understood factor that would change the global static
default locale to an unsupported one that would, via a SQL call to
`duckdb_tables` end up calling a locale-influenced stringstream that
would then throw.

Testing can also be done on native applying the following diff, yet to
be added as testing mode
```diff
diff --git a/test/unittest.cpp b/test/unittest.cpp
index 1c04f98..a70847a2a6 100644
--- a/test/unittest.cpp
+++ b/test/unittest.cpp
@@ -30,6 +30,8 @@ int main(int argc, char *argv[]) {
        duckdb::unique_ptr<FileSystem> fs = FileSystem::CreateLocal();
        string test_directory = DUCKDB_ROOT_DIRECTORY;
 
+       std::locale::global(std::locale("ja_JP.SJIS"));
+
        int new_argc = 0;
        auto new_argv = duckdb::unique_ptr<char *[]>(new char *[argc]);
        for (int i = 0; i < argc; i++) {
```

Also cleans up comment from previous PR review at
#17866 (comment)

Note that other streams might (and will) have the same problems, so it
would be handy to expand this further, here taking it one step further.