TetheringManager API clean up

Per API review:
- @IntDef defined on the type integer parameter
- have getters on each parameter that is set in the
  TetheringRequest.Builder
- new added API should not be deprecated
Below APIs is moved from system-current to module-lib-current that only
plafrom code(e.g. ConnectivityManager and Settings) can use them.
TetheringRequest.
onTetherableInterfaceRegexpsChanged, TetheringInterfaceRegexps:
Only platform code can use them because interfaces by regular
expressions are a mechanism which is planning to be deprecated.

Also rename some constants for easier to understand.

Bug: 149858697
Bug: 151243337
Test: m doc-comment-check-docs
      atest TetheringTests
Change-Id: I45cb21d5bc919f6d32c42650326597d5173ea028
Merged-In: Idd041f0fbeca411ea23e49786a50dd7feb77ef45