In order to reduce the overhead of codegen, this PR switch to use Janino to compile SQL expressions into bytecode.

After this, the time used to compile a SQL expression is decreased from 100ms to 5ms, which is necessary to turn on codegen for general workload, also tests.

cc rxin

Author: Davies Liu <davies@databricks.com>

Closes #6479 from davies/janino and squashes the following commits:

cc689f5 [Davies Liu] remove globalLock
262d848 [Davies Liu] Merge branch 'master' of github.com:apache/spark into janino
eec3a33 [Davies Liu] address comments from Josh
f37c8c3 [Davies Liu] fix DecimalType and cast to String
202298b [Davies Liu] Merge branch 'master' of github.com:apache/spark into janino
a21e968 [Davies Liu] fix style
0ed3dc6 [Davies Liu] Merge branch 'master' of github.com:apache/spark into janino
551a851 [Davies Liu] fix tests
c3bdffa [Davies Liu] remove print
6089ce5 [Davies Liu] change logging level
7e46ac3 [Davies Liu] fix style
d8f0f6c [Davies Liu] Merge branch 'master' of github.com:apache/spark into janino
da4926a [Davies Liu] fix tests
03660f3 [Davies Liu] WIP: use Janino to compile Java source
f2629cd [Davies Liu] Merge branch 'master' of github.com:apache/spark into janino
f7d66cf [Davies Liu] use template based string for codegen