JVM IR: clear BindingContext after psi2ir

This helps to reduce peak memory in lowerings/codegen by a lot.

A more robust approach would be to have a separate BindingContext for
each file, and clear each of them after running psi2ir on it. This would
also lower peak memory usage in psi2ir.

Provide a fallback workaround compiler argument
-Xir-do-not-clear-binding-context just in case BindingContext is in fact
used somewhere and it's not caught by tests.

compiler/testData/cli/jvm/extraHelp.out

@@ -19,6 +19,8 @@ where advanced options include:
                              'enable' since language version 1.3
   -Xdump-declarations-to=<path> Path to JSON file to dump Java to Kotlin declaration mappings
   -Xdisable-standard-script  Disable standard kotlin script support
+  -Xir-do-not-clear-binding-context
+                             When using the IR backend, do not clear BindingContext between psi2ir and lowerings
   -Xemit-jvm-type-annotations Emit JVM type annotations in bytecode
   -Xfriend-paths=<path>      Paths to output directories for friend modules (whose internals should be visible)
   -Xmultifile-parts-inherit  Compile multifile classes as a hierarchy of parts and facade