Align naming conventions with Android

[SebastianAigner]

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MOKO-R's naming slightly different from the Android resources counterpart, which can cause some hiccups for developers migrating from Android to Multiplatform. Some parts that are affected:

• MR.strings instead of R.string
• base instead of string directory name
• fonts instead of font directory name
• @Composable fontFamilyResource function instead of plain FontFamily() functions (that can be called outside of Composables)

Aligning these names would make it easier for developers to migrate, and could avoid some papercuts.

Likely, keeping some backwards compatibility for existing projects would be useful.