Optimize SystemEnvPropertySource when possible

Update SystemEnvironmentPropertySource to attempt optimized Map lookups
first, and only fall-back to the defensive SecurityManager safe-mode
if these fail.

Issue: SPR-12224
Optimize ReflectionUtils.isCglibRenamedMethod

Optimize ReflectionUtils.isCglibRenamedMethod by removing the regular
expression.

Issue: SPR-12227