[MCM-29] All files in behaviour_pack/entities parsed as JSON

All files within the entities folder of a behaviour pack are parsed as JSON irrespective of file name or file type. Example below from the crash log when a file called "valid_modules.txt" was included in the entities folder. The contents of said file is just plain text

This has been tested and produces the following in builds 332621 and 346553

[3728:6684] - ERROR UNKNOWN 
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JSON Parse error in file: 78934665-ad69-45ae-9a01-0ea1efe8af02:entities/valid modules.txt
* Line 1, Column 1
  Syntax error: value, object or array expected.

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[3728:6684] - ERROR UNKNOWN Assertion failed: Invalid JSON
Condition is false: false
Function: JSONReadVerifier::verifyRead in c:\DarwinWork\10\s\handheld\project\VS2015\Minecraft\Minecraft.Shared\..\..\..\..\src\common\util\JSONReadVerifier.cpp @ 30