Unifying CN and JP 辶 component

### Prerequisites

* [/] If you are reporting an issue that affects glyphs for characters for a particular region or regions, did you verify that the characters are within the supported scope of the region or regions? This generally means GB 18030 or Tōngyòng Guīfàn Hànzìbiǎo (通用规范汉字表) for China, Big Five or CNS 11643 Planes 1 & 2 for Taiwan, HKSCS-2016 for Hong Kong, JIS X 0208, JIS X 0212, and JIS X 0213 for Japan, and KS X 1001 and KS X 1002 for Korea.
* [/] Did you thoroughly search the [open](https://github.com/adobe-fonts/source-han-sans/issues) and [closed](https://github.com/adobe-fonts/source-han-sans/issues?q=is%3Aissue+is%3Aclosed) issues to avoid reporting a duplicate issue?
* [/] Did you go through the [official font readme file](https://github.com/adobe-fonts/source-han-sans/raw/release/SourceHanSansReadMe.pdf) to better understand the scope of the project, to include the *Known Issues* section at the very end?

### Description

I would like to raise the 辶 component from [this discussion](https://github.com/adobe-fonts/source-han-sans/issues/98#issuecomment-94805891) again. I think that the CN and JP glyphs for 辶 component should be unified in Source Han Sans (and to Source Han Serif).

I do know that this was rejected by Ken Lunde after consultation with the designer team (probably from Changzhou Sinotype at the time) but there is now a new team from Arphic Technology working with Adobe and thus I would suggest consulting this decision with both Changzhou Sinotype and Arphic Technology.

The points are as follow:

1. There are no official documentation or mentions of 辶 to be designed as a single stroke in any of the official documents from Tōngyòng Guīfàn Hànzìbiǎo, or any of its predecessors. Similar decisions with official documentation in say, Standard Form of National Characters, which mentioned that the two strokes in 立 and 豆 should be touching both top and bottom line, are not even implemented in Source Han Sans.
2. 辶 is designed similar to JP in some SC fonts, such as Microsoft YaHei (Windows default system font). The current design of 辶 is mainly a relic from the Shanghai Song style.
3. Sharing of 辶 glyph between CN and JP can reduce a significant amount of CIDs to be used for expanding the character set.

This suggestion should be considered by both Changzhou Sinotype and Arphic Technology as they may have better knowledge on this issue.