[plugin cli] Fix file:/// paths on Windows

[jbudz]

Parsing an absolute file path using file:/// on Windows keeps the leading slash and causes the path to not resolve correctly. This also adds a deprecation warning for paths on Windows with two slashes.

Closes #9301
Closes #8933
Closes #7133

[jbudz]

jenkins, test this

[epixa]

By "break file:// paths", do you mean that using 2 slashes on windows will no longer work?

[jbudz]

Yeah. I can make the regex more specific to only remove the leading / if it's followed by a drive letter if we want to keep supporting file://.

[epixa]

We probably should preserve the existing functionality for 5.x and remove the support for // in 6.0.

[mayyamus]

@jbudz I think it is not strict, must check string format,like follow :
0. path.length >=3
1.path.charCodeAt(0) is slash('/')
2.path.charCodeAt(1) is windows drive letters
3.path.charCodeAt(2) is ':'
if all passed,then is local file.so should strip the leading slash('/')

[LeeDr]

I haven't tested this PR, but just wondering if we can just add a catch that does the path slash manipulation only if the file is not found?

[epixa]

@LeeDr When would a file be found on windows using 3 slashes?

[LeeDr]

@epixa I was suggesting that if the user gives this incorrect syntax for Windows

file://c:/path/to/x-pack-5.0.0.zip but it currently works, we leave that as-is.

And if the user gives this correct syntax for Windows

file:///c:/path/to/x-pack-5.0.0.zip and it fails to open the file we catch that and replace /// with // and try again.

[mayyamus]

@epixa @jbudz @LeeDr for incorrect syntax(file://),we should give tips or warnings. a plan not support incorrect syntax should be scheduled.if not,wrong will be right. right is right,wrong is wrong.

[tylersmalley]

LGTM - verified I am getting the deprecation warning for file://

[kobelb]

LGTM -- tested on Windows