Omit default values in JSON dumps

The following values are omitted in JSON dumps:
- false
- 0
- empty string
- empty array
- AccessSpecifierIR::PublicAccess
- RecordTypeIR::RecordKind::struct_kind
- VTableComponentIR::Kind::FunctionPointer
- ElfSymbolIR::ElfSymbolBinding::Global

Bug: 112877706
Test: ./test.py
Change-Id: Ifef38ab9909258831ee9750c71e0513d7b56fca0
8 files changed