[lldb] Add BytecodeSection class to formatter_bytecode.py (#183876)
Changes `formatter_bytecode.compile_file` to return a `BytecodeSection`
value. The `BytecodeSection` holds the data that needs to be emitted to
an `__lldbformatters` section.
The `BytecodeSection` currently provides `write_binary`, but will be
updated in a follow up commit to include `write_source` which will allow
the data to be emitted as C source code, or Swift source code. This will
make it easier to integrate into build systems, as it's easier to get
data into a binary via source code, than as a raw binary file.