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ARROW-6351: [Ruby] Improve Arrow#values performance

Type       | Before    | After       | Speedup ratio
---------- | --------- | ----------- | -------------
Boolean    | 100.9 i/s | 34711.9 i/s | 343.87x
Decimal128 |  70.1 i/s |   660.7 i/s |   9.42x
Dictionary |  59.1 i/s |  8542.6 i/s | 144.54x
Int64      | 101.8 i/s | 41414.1 i/s | 406.72x
String     |  96.3 i/s | 17146.7 i/s | 178.13x
Timestamp  |  85.9 i/s |  1402.6 i/s |  16.32x

See ruby/red-arrow/benchmark/values/ for benchmark details.

This also adds ChunkedArray#values.

ruby/red-arrow/ext/arrow/converters.*:
ruby/red-arrow/ext/arrow/raw-records.cpp:

It extracts convert related features from raw-records.cpp to
converters.*. raw-records.cpp just uses convert related features
extracted to converters.*. The logic for convert related features
aren't changed.

ruby/red-arrow/ext/arrow/values.cpp:

It just uses extracted convert related features.

ruby/red-arrow/lib/arrow/loader.rb:

It maps the original Arrow::Array#values to Arrow::Array#raw_values to
use Arrow::Array#values defined in ruby/red-arrow/ext/arrow/arrow.cpp.

ruby/red-arrow/lib/arrow/array.rb:

It changes to fast Arrow::Array#values for Arrow::Array#to_a instead
of Enumerable#to_a.

ruby/red-arrow/benchmark/raw-records/:

Faker API is changed since Faker 2.0.0. This change uses the new
Faker API.

Closes #5194 from kou/ruby-raw-values and squashes the following commits:

b8a5a19af <Sutou Kouhei> Extract common codes as Converter
f4c113a55 <Sutou Kouhei> Remove needless "Raw" prefix
268b0474f <Sutou Kouhei>  Improve Arrow#values performance

Authored-by: Sutou Kouhei <kou@clear-code.com>
Signed-off-by: Yosuke Shiro <yosuke.shiro615@gmail.com>