PR: feat(language-service): integrate progressive init with pull-based diagnostics

Description

Integrates Progressive Project Initialization (#66966) with Pull-Based Diagnostics (#66700) so they work optimally together.

When pull-based diagnostics (LSP 3.17) is active, progressive project initialization now sends a single workspace/diagnostic/refresh notification instead of computing and pushing diagnostics for each open file. This eliminates wasted computation since the pull-based client would discard pushed diagnostics anyway.

Falls back to the chunked push-based approach when pull diagnostics is not supported by the client.

Problem

Without this integration, when both features are active:

1. Progressive init computes diagnostics for each open file (getSemanticDiagnostics) and pushes them via connection.sendDiagnostics()
2. The pull-based client ignores these pushed diagnostics (it uses textDocument/diagnostic to request them on-demand)
3. The diagnostic computation in step 1 is entirely wasted

Solution

private async initializeProjectProgressively(project: ts.server.Project): Promise<void> {
    // ...
    if (this.usePullDiagnostics) {
        // Just notify the client to re-pull — no computation needed
        this.connection.languages.diagnostics.refresh();
        return;
    }
    // Fall back to chunked push-based approach
    // ...
}

When usePullDiagnostics is true, the method:

1. Sends workspace/diagnostic/refresh to the client
2. Returns immediately — no file-by-file diagnostic computation

The client then pulls diagnostics on its own schedule, using the pull diagnostics handler which has its own caching via resultId.

Changes

Dependencies

This PR must be merged AFTER both base PRs:

• feat(language-service): implement pull-based diagnostics (LSP 3.17) #66700 — Pull-Based Diagnostics (provides usePullDiagnostics flag and workspace/diagnostic/refresh)
• perf(language-service): progressive project initialization #66966 — Progressive Project Initialization (provides initializeProjectProgressively())

Testing

• All language service tests pass (modern + legacy)
• All LSP integration tests pass (including pull diagnostics tests)
• All server unit tests pass

Breaking Changes

None

AI Disclosure

This PR was developed using Claude Opus 4 AI assistant under human orchestration and review by @kbrilla.