Introduce new manifest elements for purpose declaration.

For the purpose declaration effort, the following new manifest elements
are being introduced:
- requiresPurpose attribute for <permission>
- <valid-purpose> child tag with name attribute under <permission>
- <purpose> child tag with name, minSdkVersion, and maxSdkVersion
  attributes under <uses-permission>

Bug: 412443416
Test: m -j99
Flag: EXEMPT no public-staging.xml changes
Change-Id: Iecbc5e41fd1c12c83b5fa19889f0490f7d574218