dx: Add support for invoke-custom

This change adds the translations to invoke-custom and extends the DEX
file sections that dx emits sections for method handles and call
sites.

Test: dx/tests/run-test 135
Test: dx/testse/run-all-tests
Bug: 36641082
Bug: 36957105
Change-Id: Ia1c5b548755485755e8bab0a8f99bd745c2960cd