Resolve token count <-> token throughput inconsistency in Model Garden dashboards

[yqlu]

See b/488088173 for more context:

• Under "Throughput" section, update "Token throughput by model" chart title to be "Token count by model" (and take away the input filter)
• Under "Tokens and characters", update table to show throughput / input tokens / output tokens as three separate columns
• Under "Tokens and characters", add separate charts for "Token throughput by model" and "Token count by model" in the same dropdown