Optimizing: Rewrite blocked registers handling.

Use bitmasks (`uint32_t`) instead of `bool` arrays. Move the
blocked register initialization to the codegen constructors.

Remove dead function `BlockIfInRegister()`.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: run-gtests.sh
Test: testrunner.py --target --optimizing
Bug: 438388740
Flag: EXEMPT refactor
Change-Id: Ifb66baecb70666f021c925d233f95d185e361b2f