[FE] Web IDE: Move Web Terminal to Core

What does this MR do?

Moves IDE modules terminal and terminal_sync to Core.

Issues:

• #211685 (closed)
• #211686 (closed)

To test this issue out on GDK, you should have the Web Terminal set up. Additionally this must be tested on CE, by either deleting the ee/ directory or by setting the FOSS_ONLY environment variable to something that evaluates as true. See more info here.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team