[C++] Define minimalist C structs for exposing Arrow data types to C code

[asfimport]

This can also accompany an alternate IPC loader which does not use shared_ptr<Buffer> or other currently-in-use tools for RAII-based object lifetime.

For example, we would be able to expose arrow::StringArray to C code in a struct like

typedef struct {
  int64_t length;
  int64_t offset;
  int64_t null_count;
  const uint8_t* valid_bits;
} arrow_array_t;

typedef struct {
  struct arrow_array_t base;
  const int32_t* offsets;
  const uint8_t* data;
} arrow_string_array_t;

Reporter: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-1058. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
At some point I think it would be a good idea to create a complete implementation of data structures and IPC (which can use flatcc) in ANSI C or C99

[asfimport]

Wes McKinney / @wesm:
This issue is probably superseded by the C API work

[asfimport]

Wes McKinney / @wesm:
This was addressed by the C Data Interface