Fix resolution of percent-encoded schema paths in modelines

[shin19991207]

What does this PR do?

Prevents percent-encoded schema paths in modelines from being encoded a second time when converted to file URIs.

For example, this following percent-encoded modeline should resolve to a schema named encoded:schema.json:

# yaml-language-server: $schema=./encoded%3Aschema.json

Previously, the existing percent escape was encoded again:

./encoded%3Aschema.json
        ↓
file:///.../encoded%253Aschema.json

Consequently, the schema request targeted a file literally named encoded%3Aschema.json instead of decoding %3A to :.

What issues does this PR fix or reference?

Related to redhat-developer/vscode-yaml#1274
This is a separate modeline path case discovered while investigating encoded schema URIs in yaml.schemas.

Is it tested? How?

• New automated tests
• Tested manually:
  1. Created a schema named encoded:schema.json (For Windows, use encoded schema.json because : is invalid in filenames on Windows)
  2. Create a yaml file with a percent-encoded modeline that points to the file # yaml-language-server: $schema=./encoded%3Aschema.json (or # yaml-language-server: $schema=./encoded%20schema.json for Windows)
  3. Expect the yaml to resolve against the schema correctly

[datho7561]

Tried this out on Linux and it was working well; I'll also check it on Windows before approving...

[datho7561]

Works on Windows too!

[datho7561]

Thanks, Morgan!