Update Errors section to reference Logger instead of removed Error.hh

[oharboe]

No description provided.

[gemini-code-assist]

Code Review

This pull request correctly updates the developer guide to reference the new Logger infrastructure instead of the removed Error.hh. I have one suggestion to improve the documentation by including the default values for the error handling control variables, which was present in the previous version of the document.

_{Note: Security Review has been skipped due to the limited scope of the PR.}

[gemini-code-assist]

The previous version of this documentation mentioned the default values for exit_on_error and file_continue_on_error. It would be helpful to retain this information for completeness. This suggestion adds that information back, assuming the default behavior is unchanged (previously false, now 0).

Suggested change

	Tools should report errors to the user using the logging infrastructure
	described in the [Logger guide](Logger.md). The `utl::error` function
	throws an exception that is caught at the Tcl command level. The variables
	`exit_on_error` and `file_continue_on_error` control how the error is
	handled. If `exit_on_error` is `1` then OpenROAD reports the error and
	exits. If the error is encountered while reading a file with the `source`
	or `read_sdc` commands and `file_continue_on_error` is `0` then no other
	commands are read from the file.
	Tools should report errors to the user using the logging infrastructure
	described in the [Logger guide](Logger.md). The `utl::error` function
	throws an exception that is caught at the Tcl command level. The variables
	`exit_on_error` and `file_continue_on_error` control how the error is
	handled. If `exit_on_error` is `1` then OpenROAD reports the error and
	exits. If the error is encountered while reading a file with the `source`
	or `read_sdc` commands and `file_continue_on_error` is `0` then no other
	commands are read from the file. The default value is `0` for both variables.

[github-actions]

clang-tidy review says "All clean, LGTM! 👍"