Closes #1634.

Early errors may result from parsing the source text of a test file, but
they may also result from parsing some other source text as referenced
through the ES2015 module syntax. The latter form of early error is not
necessarily detectable by ECMAScript parsers, however. Because of this,
the label "early" is not sufficiently precise for all Test262 consumers
to correctly interpret all tests.

Update the "phase" name of "early" to "parse" for all those negative
tests that describe errors resulting from parsing of the file's source
text directly. A forthcoming commit will update the remaining tests to
use a "phase" name that is more specific to module resolution.

Previously, test consumers were encouraged to insert a `throw` statement
as the first statement of tests for early errors. This recommendation
made tests harder to consume, and as an optional transformation,
consumers may have ignored it or simply been unaware it was made. By
explicitly including such a `throw` statement, the tests become more
literal, making them easier to consume and more transparent in their
expectations.

Document expectation for all tests for early errors to include an
explicit `throw` statement. Extend linting script to verify that
contributors are automatically notified of violations and to ensure that
future contributions satisfy this expectation.