Replace stdlib on Slang API with CoreModule

[jkwak-work]

This is a breaking change in a way that the Slang API function names are changed. All of them are commented as "experimental" and we wouldn't provide a back-ward compatibility for them.

Following functions are renamed:

• compileStdLib() -> compileCoreModule()
• loadStdLib() -> loadCoreModule()
• saveStdLib() -> saveCoreModule()
• slang_createGlobalSessionWithoutStdLib() -> slang_createGlobalSessionWithoutCoreModule()
• slang_getEmbeddedStdLib() -> slang_getEmbeddedCoreModule()
• hasDeferredStdLib() -> hasDeferredCoreModule()

Following command-line arguments are renamed:

• "-load-stdlib" -> "-load-core-module"
• "-save-stdlib" -> "-save-core-module"
• "-save-stdlib-bin-source" -> "-save-core-module-bin-source"
• "-compile-stdlib" -> "-compile-core-module"

[csyonghe]

-load-stdlib should be -load-core-module.

All current mention of stdlib in the compiler codebase should be changed to core-module. There should be no mention of standard modules in any of our source code files because everything we have is jsut the core module.

[jkwak-work]

-load-stdlib should be -load-core-module.

All current mention of stdlib in the compiler codebase should be changed to core-module. There should be no mention of standard modules in any of our source code files because everything we have is jsut the core module.

I will change as suggested.

[csyonghe]

Also need to update docs/build_reference.ps1. (just change the slangc argument in the script).

[jkwak-work]

This PR is for #5335 but it doesn't close.
This PR is limited to "breaking changes".
I still need to work more on the issue.