improve performance of glTFLoader._applyExtensions

[Starryi]

Cache extensions by _getActiveExtensionsHasOwnFunction

for a specific function name, cache extensions which are enabled and have the specific function， avoid repeated traversals

ILoaderProperty._activeLoaderExtensionFunctions

use Map to replace {} for ILoaderProperty._activeLoaderExtensionFunctions, to imporve has/set/delete operation

for specific p and fName, Just ensure avoid recursive call of applyExtension(p, fName, ...)

Let's say there is an enabled extension which name is extensionA and has function loadSomeAsyc.

For a specific property p,

First, applyExtension(p, fName, ...) should not be called recursively.
In other words, the following trace should not occur:

applyExtension(p, 'loadSomeAsyc') 

             -> ... 

                   -> applyExtension(p, 'loadSomeAsyc') 

                            -> ... 

Second, extensionA.loadSomeAsyc(p, ...) should not be called recursively.
In other words, the following trace should not occur:

applyExtension(p, 'loadSomeAsyc') 

       -> extensionA.loadSomeAsyc(p) 

             -> ... 

                   -> applyExtension(p, 'loadSomeAsyc') 

                         -> extensionA.loadSomeAsyc(p)

                                 -> ... 

so, just ensue no recursive call of applyExtension(p, 'loadSomeAsyc'), two goals can be achieved at the same time.

[bjsplat]

Please make sure to label your PR with "bug", "new feature" or "breaking change" label(s).
To prevent this PR from going to the changelog marked it with the "skip changelog" label.

[bjsplat]

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[bjsplat]

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[bjsplat]

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[bjsplat]

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[bjsplat]

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[bghgary]

Thanks for the PR. Just curious, have you seen measurable performance issues with this code?

@alexchuber also recently identified an issue with the loader extension ordering that needs to be addressed. It might be good to think about both of these issues together before making a complete fix for both as they will likely touch the same code.