Fix ClearKey Drm base64 en/decoding to use base64url.

ClearKey's base64  en/decoding should use '-' and '_'
instead of '+' and '/' (web safe coding). Add support
for base64url coding in libstagefright foundation library
and update ClearKey plugins.

Test: CTS - ClearSystemTests
  ANDROID_BUILD_droid-cts/tools/cts-tradefed run cts -m
  CtsMediaTestCases --test android.media.cts.ClearKeySystemTest

Test: CTS - NativeClearSystemTests
  ANDROID_BUILD_droid-cts/tools/cts-tradefed run cts -m
  CtsMediaTestCases --test android.media.cts.NativeClearKeySystemTest

Test: libstagefright/foundation/tests/Base64_test
  adb shell /data/nativetest64/sf_foundation_test/sf_foundation_test

Test: ClearKeyDrmUnitTest
  adb shell LD_LIBRARY_PATH="/vendor/lib/mediadrm"
  /data/nativetest/ClearKeyDrmUnitTest/ClearKeyDrmUnitTest

Test: Vts
  vts-tradefed run commandAndExit vts -m VtsHalDrmV1_0Target
  --primary-abi-only -l VERBOSE

bug: 64388098
Change-Id: Ic08515fd491f15e088600c64603149401c117f4a