language cleanups

[tetron]

Goal: move essential features from "Requirement" to regular features, and make optional the requirements that only exist to indicate a certain feature is used in the document.

Command line tool

InitialWorkDirRequirement

Becomes "initialWorkDir" optional field of CommandLineTool, with the same schema and semantics as InitialWorkDirRequirement "listing" field.

EnvVarRequirement

Becomes "envDef" optional field of CommandLineTool, with same schema and sematics as EnvVarRequirement "envDef".

NetworkAccess

Becomes "networkAccess" optional field of CommandLineTool, with same schema and sematics as NetworkAccess "networkAccess".

ShellCommandRequirement

See #44

Workflows

SubworkflowFeatureRequirement

This becomes optional. This feature is allowed by default.

ScatterFeatureRequirement

This becomes optional. This feature is allowed by default.

MultipleInputFeatureRequirement

This becomes optional. This feature is allowed by default.

StepInputExpressionRequirement

This becomes optional. This feature is allowed by default.

[mr-c]

Yes, if we add feature detection to https://github.com/common-workflow-language/cwl-upgrader for @tom-tan and others to use as a reference