Implement support for explicit cached page invalidation

[cberner]

According to the libfuse docs, when FUSE_CAP_EXPLICIT_INVAL_DATA is set:

/**
 * Indicates support for invalidating cached pages only on explicit request.
 *
 * If this flag is set in the `capable` field of the `fuse_conn_info` structure,
 * then the FUSE kernel module supports invalidating cached pages only on
 * explicit request by the filesystem through fuse_lowlevel_notify_inval_inode()
 * or fuse_invalidate_path().
 *
 * By setting this flag in the `want` field of the `fuse_conn_info` structure,
 * the filesystem is responsible for invalidating cached pages through explicit
 * requests to the kernel.
 *
 * Note that setting this flag does not prevent the cached pages from being
 * flushed by OS itself and/or through user actions.
 *
 * Note that if both FUSE_CAP_EXPLICIT_INVAL_DATA and FUSE_CAP_AUTO_INVAL_DATA
 * are set in the `capable` field of the `fuse_conn_info` structure then
 * FUSE_CAP_AUTO_INVAL_DATA takes precedence.
 *
 * This feature is disabled by default.
 */