Unify command mode parameter syntax

[elliVM]

Description
Handle parameters using both option value and option=value syntax or chose a unified syntax and use only that

Use case or motivation behind the feature request
Some options require use of = while others only accept without it.

For example in file COMMAND_TERAGREP_MODE.g4 both are present

COMMAND_TERAGREP_MODE_OUTPUT: 'output' -> pushMode(GET_FIELD);
COMMAND_TERAGREP_MODE_REGEX: 'regex' -> pushMode(GET_STRING);
COMMAND_TERAGREP_MODE_ESTIMATES: 'estimates' -> pushMode(GET_FIELD);
COMMAND_TERAGREP_MODE_HEADER: 'header=' -> pushMode(GET_BOOLEAN);
COMMAND_TERAGREP_MODE_SCHEMA: 'schema=' -> pushMode(GET_STRING);

Additional context
allow for both possibly like:
COMMAND_EXAMPLE_MODE: 'value' '='? -> pushMode(GET_STRING)