[threads] remove const constructor from C(Exclusive|Shared|Single)Lock

[Rechi]

Description

Instead of casting constness away, mark the lock variables mutable if they are used in const functions.

Motivation and Context

Although casting away the constness of CCriticalSection is allowed in this cases (as the variables aren't declared as const), it still is a hack.

How Has This Been Tested?

compiled for android, ios, linux, osx and windows

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[ksooo]

Hmm, seems you made a lot of (all?) critical sections members mutable, but where are all the const_casts you wanted to eliminate?