fix(sql): minor improvements and fixes

[alespour]

This PR contains minor improvement and fixes to 'sql` package:

• return error with codes.Invalid instead of codes.Internal from translationFunc for unsupported types
• fix TUint mapping for MySQL from BIGINT to BIGINT UNSIGNED
• move invariant code out of loop in to.go: CreateInsertComponents(), remove unused map labels
• move flux->db type map out of translationFunc and use direct type comparison instead of string representation
• mssql/Azure:
  • update deps to version that bring new API + builds with Go 1.12 + does not introduce new deps (supersedes PR chore: update ms-sql/Azure deps #3172)
  • replace code duplicated from Azure go-autorest with function introduced in recent version (contributed via Expose OAuth token provider for use outside autorest Azure/go-autorest#520)

Done checklist

• Test cases written