Avoid using a separate origin for temporary variables introduced
for for loops. That doesn't add anything and gives one more case
for optimizations to deal with.
Extend the JVM specific optimizations to remove temporary
variables to deal with more cases encountered in for loops
lowering.
All bytecode text tests are run with stdlib in the classpath and only
for JVM backend, therefore directives WITH_RUNTIME, TARGET_BACKEND,
IGNORE_BACKEND are not needed
For-in-string loop can be generated using specialized 'length' and
'charAt' method calls, and with cached string length.
Note that update of the string variable in loop body doesn't affect
loop execution semantics.
#KT-21322 Fixed Target versions 1.2.20
