feat: format fixed files with the same formatters as the issues related to formatting

[ldez]

Currently (since the PR about formatters) the reports related to formatting are handled by a dedicated processor, but the suggested fixes can produce formatting issues.
Inside the fixer, golangci-lint always calls the std formatter but it's better if it calls the formatters from the configuration too.

This PR also improves performance by formatting the files only one time, and by using fileCache instead of os.ReadFile to get the file content.

Note: the formatter processor is merged with the fixer.

This improves cases that can produce missing imports.

Example

linters:
  disable-all: true
  enable:
    - err113
    - goimports

package main

func Foo(e1, e2 error) bool {
	return e1 == e2
}

The command:

./golangci-lint run --fix

Before this PR, the result is:

package testdata

func Foo(e1, e2 error) bool {
	return errors.Is(e1, e2)
}

with this PR:

package testdata

import "errors"

func Foo(e1, e2 error) bool {
	return errors.Is(e1, e2)
}

because goimports fixes imports.

Related to #5232, #5246

[ldez]

To follow the release plan, I will exceptionally merge this PR.