Use null instead of [] for ops with no args.

This reduces peak RSS on one test file from ~600 to ~560 MiB.
Refactoring text layer builder
Convert the text layer builder to a class
Refactoring PDFFindController in the text layer builder
Merge pull request #4982 from nnethercote/use-null-for-zero-args

Use null instead of [] for ops with no args.
Removing unnecessary includes from text selection example
Merge pull request #4991 from timvandermeij/text-layer-builder-refactoring

Refactoring text layer builder and converting text layer builder to a class