Is it possible to combine several template files togather and make single integrated template instead? For example to render a simple form like search block should be invoked 8 different templates like below and each of this template only has one or few line of code, see below:

region.html.twig
└─ block.html.twig
   └─ form.html.twig
      ├─ form-element.html.twig
      |  ├─ form-element-label.html.twig
      |  └─ input.html.twig
      └─ container.html.twig
          └─ input.html.twig


As you can see in below some of this files Just have a few line of code:
region.html.twig

{% if content %}
  &lt;div{{ attributes }}&gt;
    {{ content }}
  &lt;/div&gt;
{% endif %}


form.html.twig

&lt;form{{ attributes }}&gt;
  {{ children }}
&lt;/form&gt;


form-element.html.twig

{% if title is not empty or required -%}
  &lt;label{{ attributes.addClass(classes) }}&gt;{{ title }}&lt;/label&gt;
{%- endif %}


input.html.twig

&lt;input{{ attributes }} /&gt;{{ children }}


container.html.twig

&lt;div{{ attributes.addClass(classes) }}&gt;{{ children }}&lt;/div&gt;



Some of this templates files are common with other parts of page and
editing each of them can affect to other parts and cause unwanted changes
. for example in this case drupal theme system for: "input.html.twig", suggest only input--submit.html.twig and this suggestion also common between search block and search form.
Editing and managing this template files is tedious and difficult and
make my theme folder busy.
Most of these templates have ambiguity and unclear content code


For this reason I'm looking for a method to combine this template files and make one template file like "form--search-block.html.twig" to I can edit all element needs for rendering a form in one special place 
and with more flexibility and confidently.
In drupal 8 there's this rule called theme inheritance and backward compatibility, what you have to do to accomplish what you want is to make sure that your subtheme does not inherit any core theme's HOOKS

You might want to play around in your subtheme and set your base theme to null
I haven't checked it myself but it might work.

And then of course you have to define new preprocess templating rules in your themename.theme file using theme_suggestions_page_alter function, you can read more here

Then based on what you defined in your .theme file you may proceed with creating a unified template file

Also you might want to read this suggestion that somewhat explains a similar use case