refactor: Improve XML performance

[kitadai31]

Improve the performance of XML operations by not calling node.getChildNodes() multiple times in a loop.

The result of node.getChildNodes() should be stored in a variable before starting a for loop.

I compared the performance before PR and after PR, using a Snapdragon 662+4GB RAM phone and a Snapdragon 410+2GB RAM phone
This resulted in significant improvements for some XML files, especially those with many child nodes.

https://github.com/inotia00/revanced-patches/blob/b1776cf00729216c001a8dc6720468c08666936d/patches/src/main/kotlin/app/revanced/patches/youtube/layout/theme/ThemePatch.kt#L79-L90
[res/values/colors.xml]
SD662: 637 ms -> 3 ms
SD410: 2971 ms -> 6 ms

https://github.com/inotia00/revanced-patches/blob/b1776cf00729216c001a8dc6720468c08666936d/patches/src/main/kotlin/app/revanced/patches/youtube/utils/settings/SettingsPatch.kt#L227-L244
[res/values/styles.xml]
SD662: 1107 ms -> 10 ms
SD410: 6401 ms -> 35 ms

https://github.com/inotia00/revanced-patches/blob/b1776cf00729216c001a8dc6720468c08666936d/patches/src/main/kotlin/app/revanced/patches/youtube/general/snackbar/SnackBarComponentsPatch.kt#L350-L361
[res/values/dimens.xml]
SD662: 4837 ms -> 11 ms
SD410: 24929 ms -> 13 ms

In addition, I did some refactoring:

• Usually, to get the root node of a document, use document.getDocumentElement()
• Avoid iterating one XML twice
• break a for loop if possible

I tested this change with 19.44.36, 19.16.36, and 18.29.36 and confirmed that this changes don't change the result resources.
I compared the patched-temporary-files dir of current patches and my PR branch patches using WinMerge and those were identical.

[inotia00]

This PR includes a small refactoring for ResourcePatch.

Can this PR includes a class java.nio.file.Files check for Android 5 - 7?

[kitadai31]

No, I was just going to push a second PR that is for A5-7 support

[inotia00]

Thanks