iwa: Add DoNotFakeInstallPage and DoNotTrustKey traits to BundledIWA

This makes BundledIsolatedWebApp::Install automatically fake the
installation page and mark the signing key as trusted by default, and
adds optional traits to disable this behavior for tests that need it.

This also removes the InstallWithSource overload that directly takes
a IsolatedWebAppInstallSource, and adds the traits to the other
InstallWithSource overloads.

The BundledIsolatedWebApp::TrustSigningKey/FakeInstallPageState
functions are still needed by tests that are testing the install flow
itself and don't want to rely on BundledIsolatedWebApp::Install.

In a followup CL we can remove TrustBundleAndInstall.

Bug: 390443309
Change-Id: Ic99f4356e5085f406891eacdb404f15dd5f345ab
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6160656
Commit-Queue: Robbie McElrath <rmcelrath@chromium.org>
Reviewed-by: Andrew Rayskiy <greengrape@google.com>
Cr-Commit-Position: refs/heads/main@{#1408237}