This is a large PR which touches a lot of code.

Get rid of `PresentmentMechanism` and `PresentmentModel` and instead make
the presentment mechanisms available via simple suspend functions:

- `digitalCredentialsPresentment()` for W3C Digital Credentials presentment
- `uriSchemePresentment()` for OpenID4VP 1.0 URI Scheme presentment
- `Iso18013Presentment()` for ISO/IEC 18013-5:2021 proximity presentment.

Also introduce a new `PresentmentModel` which can be used for coupling
the mechanism with the UI/UX. Introduce `PresentmentActivity` with
nice UI and animations and use this for both NFC and QR engagement and
include it in the `AndroidManifest.xml` file for the library.

Beef up `PromptModel` so UIs can track if prompts are currently
showing. This is used in `PresentmentActivity` for moving the card to
the top when this is so. Add `PromptDialogModel.waitUntilBound()`
which is needed by `PresentmentActivity` to wait until the activity is
up and running.

Add `PromptModel.requestConsent()` to show consent screens and
`ShowConsentPromptFn` as a typealias with actual implementations
`promptModelSilentConsent()` and `promptModelRequestConsent()` where
the latter calls into `PromptModel.requestConsent()`. Make
`PresentmentSource` take a `ShowConsentPromptFn` so the application
has full control of where the consent moment happens.

Minor UI improvements in the Consent prompt.

Introduce new `Branding` object so the application can specify which
theme, app icon, and application name to use in various UI elements in
the library (for example, the consent prompt), and missing card
art. Add example use of this in Test App with a Lime Green theme which
can be set on the Settings screen.

Mark `buildXyz()` functions as inline so they work both from suspend
and normal contexts.

Make proximity presentment _always_ wait for the reader to end the
session, instead of sending the session termination along with the
response. This fixes a long-standing problem where connections are
closed too early which we worked around by long timeouts on e.g. L2CAP
sockets (causing other problems). This behavior is also recommended in
the latest ISO/IEC 18013-5 Second Edition drafts.

Fix compilation on iOS.

Test: Unit tests.
Test: Manually tested on Android and iOS.

Signed-off-by: David Zeuthen <zeuthen@google.com>