Rule for redundant error declarations

[alexandear]

Is your feature request related to a problem? Please describe.

The code

var err error
insts, err := call()

can be simplified to

insts, err := call()

Describe the solution you'd like

A new rule redundant-err-decl that would suggest removing redundant err declarations.

Describe alternatives you've considered

Use sed to search redundant for err declarations and remove them manually:

find . -name '*.go' -exec sed -n '/var err error/{N;/\n.*err :=/p;}' {} +

Additional context

See these PRs for examples:

• all: remove redundant err declarations go-delve/delve#3855
• refactor: remove redundant err declarations go-gitea/gitea#32381
• Remove redundant variable declarations vektra/mockery#829