btrfs: move large data folios out of experimental features

btrfs: move large data folios out of experimental features

This feature was introduced in v6.17 under experimental, and we had
several small bugs related to or exposed by that:

  e9e3b22ddfa7 ("btrfs: fix beyond-EOF write handling")
  18de34daa7c6 ("btrfs: truncate ordered extent when skipping writeback past i_size")

Otherwise, the feature has been frequently tested by btrfs developers.

The latest fix only arrived in v6.19. After three releases, I think it's
time to move this feature out of experimental.

And since we're here, also remove the comment about the bitmap size
limit, which is no longer relevant in the context. It will soon be
outdated for the incoming huge folio support.

Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>