[ports] Enable use of "::" to escape options separator

[ypujante]

This PR addresses the issue that there is no way to have a port option value containing a ":" since it is the option separator.

The fix is to allow the escape sequence "::" similar to "\\" in strings or "%%" in printf format strings.

Python proof of concept:

>>> s = 'abc::def'
>>> s
'abc::def'
>>> s.replace('::', '\0')
'abc\x00def'
>>> s.replace('::', '\0').replace('\0', ':')
'abc:def'

The implementation replaces :: with \0 (the char(0) NOT the character "0") before splitting and then replaces \0 with : after the split.

[ypujante]

The reported tests failures are, none of which seems to be related to my changes.

======================================================================
ERROR [61.229s]: test_offset_converter (test_browser.browser)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/root/project/test/common.py", line 2063, in run_browser
    self.assertContained(expected, output)
  File "/root/project/test/common.py", line 1393, in assertContained
    additional_info
  File "/usr/lib/python3.6/unittest/case.py", line 670, in fail
    raise self.failureException(msg)
AssertionError: Expected to find '/report_result?exit:1
' in '[no http server activity]
', diff:
======================================================================
FAIL [2.716s]: test_wasmfs_opfs_jspi (test_browser.browser)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/root/project/test/common.py", line 2063, in run_browser
    self.assertContained(expected, output)
  File "/root/project/test/common.py", line 1393, in assertContained
    additional_info
  File "/usr/lib/python3.6/unittest/case.py", line 670, in fail
    raise self.failureException(msg)
AssertionError: Expected to find '/report_result?exit:0
' in '/report_result?exception:Maximum call stack size exceeded / RangeError: Maximum call stack size exceeded    at http://localhost:8888/test.wasm:wasm-function[108]:0x6e2a    at http://localhost:8888/test.wasm:wasm-function[44]:0xf68    at http://localhost:8888/test.wasm:wasm-function[167]:0xda8d    at http://localhost:8888/test.wasm:wasm-function[127]:0xae45    at http://localhost:8888/test.wasm:wasm-function[266]:0x10681    at http://localhost:8888/test.wasm:wasm-function[197]:0xe7ce
', diff:

======================================================================
FAIL [2.653s]: test_wasmfs_opfs_jspi_wasm_bigint (test_browser.browser)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/root/project/test/common.py", line 2063, in run_browser
    self.assertContained(expected, output)
  File "/root/project/test/common.py", line 1393, in assertContained
    additional_info
  File "/usr/lib/python3.6/unittest/case.py", line 670, in fail
    raise self.failureException(msg)
AssertionError: Expected to find '/report_result?exit:0
' in '/report_result?exception:Maximum call stack size exceeded / RangeError: Maximum call stack size exceeded    at http://localhost:8888/test.wasm:wasm-function[106]:0x6ab5    at http://localhost:8888/test.wasm:wasm-function[43]:0xf5a    at http://localhost:8888/test.wasm:wasm-function[166]:0xd78a    at http://localhost:8888/test.wasm:wasm-function[125]:0xaad7    at http://localhost:8888/test.wasm:wasm-function[263]:0x10303    at http://localhost:8888/test.wasm:wasm-function[196]:0xe4c2
', diff:

[ypujante]

I merged with latest branch and all is green.