Moved issues/IssueRegistry to mimic AS convention + README for AndroidFrameworkLintChecker

Moved CallingIdentityTokenDetector's issues from IssueRegistry to itself
since this is the pattern used for built-in Android Studio checks.

Wrote README.md on how to build a lint report and how to add new lint
checks.

Bug: 192925086
Test: m out/soong/.intermediates/frameworks/base/services/accessibility/services.accessibility/android_common/lint/lint-report.html
Change-Id: I6be3d49e5eacc34cf60db125a52ae3da9174be4a