[rafayqayyum]

Motivation

Closes #2784

Hovering an HTML element in a freshly opened ERB file fails with Unable to resolve text model content for resource embedded-content://… until the file is edited. That explains why it reproduced for some people and not others.

Implementation

Document#initialize calls parse!, so after didOpen the document no longer needs parsing. The delegate/textDocument/virtualState notification in BaseServer is only sent when document.parse! returns true, which first happens after an edit, so the extension's embedded-content provider has nothing for a newly opened file.

text_document_did_open now sends the virtual state for ERB documents when the client supports request delegation. I kept this in server.rb rather than base_server.rb to avoid conflicting with #4261, which reworks the parse/notify block there (it keeps the parse!-true condition, so it doesn't cover this case).

Automated Tests

Added a server test that opens an ERB document with request delegation enabled and asserts the virtualState notification is sent with the host-language source. It fails on main (no notification is sent).

Manual Tests

1. Open this repository in VS Code so the extension uses the local server.
2. Open any .html.erb file and, without editing it, hover an HTML tag.
3. On main: the "Unable to resolve text model content" error appears. With this branch: the HTML hover shows.

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