[roll] Roll fuchsia [component] Add helpers to open directories

The `component::Connect()` and `component::ConnectAt()` are frequently
(mis)used to open `fuchsia.io` protocols like files and directories.
This only works right now as in io1, many operations - like directory
enumeration - were unprivileged. In order to start enforcing the new
io2 rights model, we need to require that callers opening directories
(or other node types) explicitly set the flags/rights they want.

To migrate clients more easily, we add helper functions
`component::OpenDirectory()` and `component::OpenDirectoryAt()` which
mirror the equivalents above, but are intended for opening directories.
By default we use the same set of flags/rights used by service
directories (`r*` or `fuchsia.io/PERM_READABLE`).  Very few if any
callers open non-directory protocols, so we leave these use cases out
of //sdk/lib/component to keep things simple.

Once all clients have migrated to these new functions, we can
statically assert that `Connect`/`ConnectAt` do not compile with
fuchsia.io protocols, and provide an error message pointing users to
`OpenDirectory`/`OpenDirectoryAt` (or an equivalent fdio function for
files/symlinks).

Remove `internal::GetGlobalServiceDirectory()` function as it is the
same as `component::GetServiceRoot()` and move flags constant used for
opening service directories in `constants.h`. Make lifetimes of strings
passed to fdio functions explicitly outlive the function calls.

Original-Bug: 324111518
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1197375
Original-Revision: 9830deb75e24e88e74d64d6eaec1b6d86c1ecf34
GitOrigin-RevId: 064d470a971803e0de9ea1ed143d0bc4e4c32c16
Change-Id: I832c71bf7b4d611aa4fdd10a27ac55c71659e3ee