ARROW-3688: [Rust] Add append_values for primitive builders
ARROW-3688: [Rust] Add append_values for primitive builders

This implements `append_values` for primitive builders, which allows for pushing a number of values and their validity buffer at the same time.

Closes #7306 from nevi-me/ARROW-3688

Authored-by: Neville Dipale <4e1ab218b24f06847d563ff3773c7517c139f863@gmail.com>
Signed-off-by: Andy Grove <f68909d51919859739a1c5d24450a2cc1026e93b@gmail.com>

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