Upstream go-mysql patches

[grodowski]

We have patched go-mysql inside vendor/ in two recent bugfixes:

• Patch go-mysql to keep trailing zero in floats in json #368
• Use 64 bit size when formatting FloatWithTrailingZero #379
• Patch fetchIndexesViaSqlDB in go-mysql to not return invisible indexes #383

This should be considered technical debt and proposed as pull requests to https://github.com/go-mysql-org/go-mysql, so that we don't accidentally lose those patches when updating deps (although all of them have test coverage)

[chenhuiyeh]

Both patches are upstreamed to go-mysql