[trace] Add an option to dump instructions in json and to a file

In order to provide simple scripting support on top of instruction traces, a simple solution is to enhance the `dump instructions` command and allow printing in json and directly to a file. The format is verbose and not space efficient, but it's not supposed to be used for really large traces, in which case the TraceCursor API is the way to go.

- add a -j option for printing the dump in json
- add a -J option for pretty printing the json output
- add a -F option for specifying an output file
- add a -a option for dumping all the instructions available starting at the initial point configured with the other flags
- add tests for all cases
- refactored the instruction dumper and abstracted the actual "printing" logic. There are two writer implementations: CLI and JSON. This made the dumper itself much more readable and maintanable

sample output:

```
(lldb) thread trace dump instructions  -t -a --id 100 -J
[
  {
    "id": 100,
    "tsc": "43591204528448966"
    "loadAddress": "0x407a91",
    "module": "a.out",
    "symbol": "void std::deque<Foo, std::allocator<Foo>>::_M_push_back_aux<Foo>(Foo&&)",
    "mnemonic": "movq",
    "source": "/usr/include/c++/8/bits/deque.tcc",
    "line": 492,
    "column": 30
  },
  ...
```

Differential Revision: https://reviews.llvm.org/D128316

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