all: Upgrade to go 1.16

[jiping-s]

go 1.16 should offer significant performance improvement in the scheduler when GOMAXPROCS is high (e.g. 1000), due to partial addressing of golang/go#28808

What need to be done:

• Running benchmarks with fixed GOMAXPROCS=12 against different inputs to make sure there is no slowdown
• Running benchmarks with GOMAXPROCS=1000 against different inputs to make sure there is no slowdown
• Running benchmarks with default GOMAXPROCS on a server with at least 500 cores to make sure there is no slowdown
• Try different defs.IntermediateBufferedChannelSize values to see if it should be changed.

Input log types:

• Common log records with around 200 bytes for each record, including syslog headers
• Huge log records for error dumps, 10-50K. The new errors-input.log may be good enough for this.

[jiping-s]

Verified, no visible improvement.