`export { ... }` blocks can get a bit long, so I thought it would make
sense to have an option that makes it so their contents are not indented
(basically the same argument as for namespaces).
This is based on the `NamespaceIndentation` option, except that there is
no option to control the behaviour of `export` blocks when nested because
nesting them doesn’t really make sense.
Additionally, brace wrapping of short `export { ... }` blocks is now controlled by the
`AllowShortBlocksOnASingleLine` option. There is no separate option just for `export`
blocks because you can just write e.g. `export int x;` instead of `export { int x; }`.
This closes#121723.
106c483a10
