feat(helper): add sass helper

[pengzhanbo]

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Provide a description in this PR that addresses what the PR is solving. If this PR is going to solve an existing issue, please reference the issue (e.g. close #123).

What is the purpose of this pull request?

• Bug fix
• New feature
• Other

Description

Input:

@use "@vuepress/helper";

:root {
  @include helper.color-palette("accent", #5086a1);
}

Output:

:root {
  --vp-c-accent: #5086a1;
  --vp-c-accent-hover: #6a9cb5;
  --vp-c-accent-bg: #8cb3c6;
  --vp-c-accent-soft: rgba(120, 165, 188, 0.2725);
}

[coveralls]

Pull Request Test Coverage Report for Build 9394401039

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 56.168%

---

Totals
Change from base Build 9381003398:	0.0%
Covered Lines:	992
Relevant Lines:	1582

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9394443394

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 56.168%

---

Totals
Change from base Build 9381003398:	0.0%
Covered Lines:	992
Relevant Lines:	1582

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9395563100

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 56.168%

---

Totals
Change from base Build 9381003398:	0.0%
Covered Lines:	992
Relevant Lines:	1582

---

💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 9395562812

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 56.168%

---

Totals
Change from base Build 9381003398:	0.0%
Covered Lines:	992
Relevant Lines:	1582

---

💛 - Coveralls

[Mister-Hope]

我的意思是跟src并列，这样你只需要在files里生明就可以了

[pengzhanbo]

我的意思是跟src并列，这样你只需要在files里生明就可以了

还是跟 client/node/shared 保持相同的层级吧，放到 src 同层级，结构上看起来有些割裂。

[coveralls]

Pull Request Test Coverage Report for Build 9400170277

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 56.168%

---

Totals
Change from base Build 9381003398:	0.0%
Covered Lines:	992
Relevant Lines:	1582

---

💛 - Coveralls

[Mister-Hope]

我的意思是跟src并列，这样你只需要在files里生明就可以了

还是跟 client/node/shared 保持相同的层级吧，放到 src 同层级，结构上看起来有些割裂。

我并不觉得他割裂，其他包已经有诸如template 这样的文件夹了。而且你也很难说他是一个需要经过编译的source