Profile memory usage of pattern vertex attributes

[karimnaaji]

As suggested by @ansis in #9372 , the layout involved by the pattern vertex attributes could be improved to prevent 4 bytes alignment hardware requirement loss.

We would have to first determine whether this layout becomes heavily used by base map styles and see how much memory is involved by it before adjusting it for packing. It can become an issue if data driven expressions are used for *-pattern, refer #9372 (comment).

[astojilj]

StructArrayLayout8ui2ub18.prototype.bytesPerElement = 18;
register('StructArrayLayout8ui2ub18', StructArrayLayout8ui2ub18);

This alignment seems problematic:

https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/OpenGLES_ProgrammingGuide/TechniquesforWorkingwithVertexData/TechniquesforWorkingwithVertexData.html#//apple_ref/doc/uid/TP40008793-CH107-SW15

[karimnaaji]

Post #9681 here are the remainder layouts that might require such attention:

 $ yarn run codegen
 Warning: The layout StructArrayLayout3ui6 is not aligned to 4-bytes boundaries.
 Warning: The layout StructArrayLayout3i6 is not aligned to 4-bytes boundaries.
 Warning: The layout StructArrayLayout3ui6 is not aligned to 4-bytes boundaries.
 Warning: The layout StructArrayLayout1ui2 is not aligned to 4-bytes boundaries.

[mourner]

Pattern attributes are reasonably compact after #12326. For other non-4-bytes-aligned attributes, let's track this in a separate issue because the title/description doesn't reflect it.