Codegen whitespace fixes
Codegen indent fixes
Codegen empty lines fix
Codegen style fix
auto merge of #4515 : brunoabinader/servo/codegen-cleanup, r=Ms2ger

Main changes:
- Whitespace (indent) fixes;
- CGIndent-related fixes;
- Removed consecutive empty lines;
- Removed empty lines before closing brackets;
- Codegen style fixes;

Tests:

We don't have a static code style analyzer yet, so I've checked using the following (together with manual lookup at some selected generated bindings):

1. Check for lines with wrong indentation (1 to 3 whitespaces at the beginning)
Command: ```$ pcregrep -r "^[ ]{1,3}[^ ]" components/script/dom/bindings/codegen/Bindings```
Expected: None
Actual: None

2. Check for lines with wrong indentation (5 to 7 whitespaces at the beginning)
Command: ```$ pcregrep -r "^[ ]{5,7}[^ ]" components/script/dom/bindings/codegen/Bindings```
Expected: None
Actual: None

3. Check for lonely semicolons
Command: ```$ pcregrep -r " \{0,\};" components/script/dom/bindings/codegen/Bindings```
Expected: None
Actual: None

4. Check for empty lines before closing brackets
Command: ```$ pcregrep -r -M "^$\n {0,}\}" components/script/dom/bindings/codegen/Bindings```
Expected: None
Actual: None

5. Check for consecutive empty lines
Command: ```$ pcregrep -r -M "^$\n^$\n" components/script/dom/bindings/codegen/Bindings```
Expected: None
Actual:
```components/script/dom/bindings/codegen/Bindings/ChildNodeBinding.rs
components/script/dom/bindings/codegen/Bindings/ElementCSSInlineStyleBinding.rs
components/script/dom/bindings/codegen/Bindings/ParentNodeBinding.rs
components/script/dom/bindings/codegen/Bindings/URLUtilsBinding.rs
components/script/dom/bindings/codegen/Bindings/URLUtilsReadOnlyBinding.rs
```
All of the above are ```[NoInterfaceObject]```, thus providing only imports. We shouldn’t, however, generate empty lines (investigate this later on).