AudioPolicyEffects: Add thread safety annotations

Modernize sp<> creation.
Clean up comments.
Regroup and update legacy effect parsing methods to be static
(but do not assume Effect .conf files are supported as they
are not used for HIDL or AIDL HALs, enforced by VTS since Android P).

Test: atest CtsMediaAudioTestCases
Bug: 317816718
Merged-In: I3eff2e555863ba2c40bce8232441e9def64e55a2
Change-Id: I3eff2e555863ba2c40bce8232441e9def64e55a2