[ECM] Update enhanced-confirmation.xml docs

    <enhanced-confirmation-trusted-package

         package="com.example.app"

         sha256-cert-digest="E9:7A:BC:2C:D1:CA:8D:58:6A:57:0B:8C:F8:60:AA:D2:8D:13:30:2A:FB:C9:00:2C:5D:53:B2:6C:09:A4:85:A0"/>

    ...

    <enhanced-confirmation-trusted-installer

         package="com.example.installer"

         sha256-cert-digest="E9:7A:BC:2C:D1:CA:8D:58:6A:57:0B:8C:F8:60:AA:D2:8D:13:30:2A:FB:C9:00:2C:5D:53:B2:6C:09:A4:85:A0"/>

    ...

The "enhanced-confirmation-trusted-package" entry shown above indicates that "com.example.app"

should be considered a "trusted package". A "trusted package" will be exempt from ECM restrictions.

The <enhanced-confirmation-trusted-package> entry shown in the above example indicates that

"com.example.app" should be considered a "trusted package". A "trusted package" will be exempt from

ECM restrictions.

The <enhanced-confirmation-trusted-installer> entry shown in the above example indicates that

"com.example.app" should be considered a "trusted installer". Apps installed by "trusted installers"

will be exempt from ECM restrictions, with conditions explained in the next few paragraphs.

If zero <enhanced-confirmation-trusted-installer> entries are declared, then *all* packages will be

exempt from ECM restrictions, except apps meeting *all* of the following criteria:

    A. The app is not pre-installed, and

    B. The app has no matching <enhanced-confirmation-trusted-package> entries declared, and

    C. The app is marked by its installer as coming from an untrustworthy package source.

(For example, an installer may set an app's package source to

PackageInstaller.PACKAGE_SOURCE_DOWNLOADED_FILE or PackageInstaller.PACKAGE_SOURCE_LOCAL_FILE,

which are considered untrustworthy.)

If one or more <enhanced-confirmation-trusted-installer> entries are declared, then packages must,

in order to be exempt from ECM, meet at least one of the following criteria:

The "enhanced-confirmation-trusted-installer" entry shown above indicates that

"com.example.installer" should be considered a "trusted installer". A "trusted installer", and all

packages that it installs, will be exempt from ECM restrictions. (There are some exceptions to this.

For example, a trusted installer, at the time of installing an app, can opt the app back in to ECM

restrictions by setting the app's package source to PackageInstaller.PACKAGE_SOURCE_DOWNLOADED_FILE

or PackageInstaller.PACKAGE_SOURCE_LOCAL_FILE.)

    A. Be installed by an installer with a matching <enhanced-confirmation-trusted-installer> entry

       declared, and be marked as coming from an "trustworthy" package source by the installer, or

    B. Be installed via a pre-installed installer, and be marked as coming from a "trustworthy"

       package source by the installer, or

    C. Have a matching <enhanced-confirmation-trusted-package> entry declared.

In either case:

For either type of XML element:

- The "package" XML attribute refers to the app's package name.

- The "sha256-cert-digest" XML attribute refers to the SHA-256 hash of an app signing certificate.

For any entry to successfully apply to a package, both XML attributes must be present, and must

match the package. That is, the package name must match the "package" attribute, and the app must be

signed by the signing certificate identified by the "sha256-cert-digest" attribute..

signed by the signing certificate identified by the "sha256-cert-digest" attribute.

-->

<config></config>