Use 21st century terms in the SDK repo

[kevmoo]

See https://developers.google.com/style/word-list RE allow/block list, master/slave alternatives etc

Will require work items across different components.

[kevmoo]

CC @vsmenon

[mit-mit]

First CL: https://dart-review.googlesource.com/c/sdk/+/150623

[mit-mit]

Second CL: https://dart-review.googlesource.com/c/sdk/+/150626

[mit-mit]

Updates in scripts: https://dart-review.googlesource.com/c/sdk/+/150629/

[mit-mit]

Runtime changes: https://dart-review.googlesource.com/c/sdk/+/150630

[mit-mit]

Test changes in https://dart-review.googlesource.com/c/sdk/+/150632