feat(pluginutils): normalizePath

[eight04]

Rollup Plugin Name: pluginutils

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

If yes, then include "BREAKING CHANGES:" in the first commit message body, followed by a description of what is breaking.

List any relevant issue numbers:

Description

This PR includes:

1. A new utility normalizePath.
2. Fixes a bug on Windows. On Windows 10, test failed because path.resolve creates patterns including backward slash \. This patch adds a normalization similar to createFilter:
   

   plugins/packages/pluginutils/src/createFilter.ts

   Lines 15 to 17 in 55a9cb2

   	const basePath = resolve(resolutionBase || '')
   	.split(sep)
   	.join('/')

3. Small quotes typo in README.

[NotWoods]

plugin-typescript has a similar function to normalize the path. Can we make that its own pluginUtil?

[shellscape]

@eight04 please take a look at the last comment

[eight04]

How does typescript plugin use the normalization? If it also relates to picomatch then we can add a compilePicomatch function.

Or, do you want a small util like this:

export function normalizePathSep(path) {
  return path
    .split(sep)
    .join('/');
}

[NotWoods]

Just a small util like that, although I prefer the implementation in the typescript plugin as it uses constants from node.

[eight04]

I think these were added by prettier.

[shellscape]