[antlr4] Update antlr4 to v4.11.1

[shybovycha]

This change updates antlr4 to the most recent version.
As a bonus, it uses GitHub instead of the website to download the sources, so it is easier to maintain in the future.

• What does your PR fix?

  N/A

• Which triplets are supported/not supported? Have you updated the CI baseline?

  Not updated

• Does your PR follow the maintainer guide?

  Yes

• If you have added/updated a port: Have you run ./vcpkg x-add-version --all and committed the result?

  Yes

[github-actions]

This is a new experimental fast check for PR issues. Please let us know if this bot is helpful!

PRs must add only one version and must not modify any published versions

When making any changes to a library, the version or port-version in vcpkg.json or CONTROL must be modified.

error: checked-in files for antlr4 have changed but the version was not updated
version: 4.11.1
old SHA: ef3bae454085da0602d52c28825a4dba6dd1ae98
new SHA: a512f8487790710cd274bc6643bd58e7999608f3
Did you remember to update the version or port version?
Use --overwrite-version to bypass this check
***No files were updated***

[github-actions]

This is a new experimental fast check for PR issues. Please let us know if this bot is helpful!

PRs must add only one version and must not modify any published versions

When making any changes to a library, the version or port-version in vcpkg.json or CONTROL must be modified.

error: checked-in files for antlr4 have changed but the version was not updated
version: 4.11.1
old SHA: ef3bae454085da0602d52c28825a4dba6dd1ae98
new SHA: a512f8487790710cd274bc6643bd58e7999608f3
Did you remember to update the version or port version?
Use --overwrite-version to bypass this check
***No files were updated***

[BillyONeal]

Thanks!