change: cmake: change style to set indent 4

Set indent 4 in all:
- cmakelint
- editorconfig
- Style Guide

Selected 4 instead of 2 as most existing files use 4 as indent. Only
these somewhat external files used indent 2 / tab.
- cmake/CopyFiles.cmake
- cmake/FindPythonModule.cmake
- cmake/GNUInstallDirs.cmake

.cmakelintrc

@@ -1,2 +1,3 @@
 # project has long lines
 filter=-linelength
+spaces=4

.editorconfig

@@ -19,3 +19,7 @@ max_line_length = 99
 [{**.yml, **.yaml, **.jinja}]
 indent_style = space
 indent_size = 4
+
+[{CMakeLists.txt,**.cmake}]
+indent_style = space
+indent_size = 4

docs/manual/developer/04_style_guide.md

@@ -508,10 +508,11 @@ or
 
 ## CMake
 
-* Shall use 2-space indentation
+* Shall use 4-space indentation
 * Shall use lower case for commands
 * Shall use commands, including `if` etc., without extra spaces before or after `(` and `)` (Eg. `command(<args>)`
 * `endif`, `endforeach`, and similar commands shall not have any arguments
+* Shall keep flowing `)` at same indentation as starting clause
 
 ## Markup Languages