GHA: add support for packaging Asserts and NoAsserts toolchain variants

Follow up to swiftlang/swift-installer-scripts#448. Adding packaging support for NoAssert toolchain in CI.
### Changes include:

    - Apply mimalloc patch to outputs of both no-asserts and asserts toolchains
    - Use matrix.variant in places where Asserts was assumed
    - Add robocopy step to fill missing binaries in NoAssert layout
    - Independently build and upload msi's for bld, cli, dbg, and ide by variant
    - Pass the ToolchainVariant flag to the installer.wixproj

Author: mhegazy