[azsystemevents] Remove gopls

[richardpark-msft]

Removing references to any tools that aren't in the standard toolset, like gopls. Keeps our setup a bit simpler for the azure-rest-api-specs repo.

Part of the fix for #25554

[Copilot]

Pull Request Overview

This PR contains code generation updates and refactoring of the internal generate tool for the azsystemevents package. The changes improve code generation by simplifying the implementation to use string-based operations instead of relying on the external gopls tool.

Key changes:

• Removed dependency on the gopls tool for code manipulation, replacing it with regex-based string operations
• Simplified the code generation flow to work entirely with in-memory strings
• Updated dependency versions (azcore v1.18.1 → v1.19.0, azinternal v1.11.1 → v1.11.2)

Reviewed Changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
sdk/messaging/eventgrid/azsystemevents/version.go	Added new version file with module metadata
sdk/messaging/eventgrid/azsystemevents/time_rfc3339.go	Reordered imports to follow standard library first convention
sdk/messaging/eventgrid/azsystemevents/time_rfc1123.go	Removed unused RFC1123 time handling code
sdk/messaging/eventgrid/azsystemevents/testdata/_metadata.json	Updated emitter version to 0.8.3
sdk/messaging/eventgrid/azsystemevents/models_serde.go	Fixed comments for internal types and reordered imports
sdk/messaging/eventgrid/azsystemevents/internal/gopls/gopls.go	Removed entire gopls package as it's no longer needed
sdk/messaging/eventgrid/azsystemevents/internal/generate/regex_helpers.go	Refactored to use string-based operations instead of file I/O
sdk/messaging/eventgrid/azsystemevents/internal/generate/generate_test.go	Refactored tests to work with strings instead of temporary files
sdk/messaging/eventgrid/azsystemevents/internal/generate/generate_constants.go	Changed to accept string input instead of file reader
sdk/messaging/eventgrid/azsystemevents/internal/generate/generate.go	Major refactoring to work with in-memory strings and simplified logic
sdk/messaging/eventgrid/azsystemevents/go.sum	Updated dependency checksums
sdk/messaging/eventgrid/azsystemevents/go.mod	Updated dependency versions
sdk/messaging/eventgrid/azsystemevents/build.go	Added gofmt step before code generation