Feature/refactor compile and link fxns

[ellosel]

Tensile and TensileCreateLibrary both invoke the function writeSolutionsAndKernels. This function is responsible for executing the "build recipe". That is, nearly all code related to code generation, compiling, linking, and bundling is contained in writeSolutionsAndKernels. This PR is a part of a larger parallelization change to TensileLt. Its objective is to improve the composability and testability of this important function.

Outcomes:

• Toolchains are created at the beginning of Tensile and TensileCreateLibrary, unifying structure and access to toolchain components.
• Toolchains have composable methods for general compile and link commands.
• processKernelSource is the code generation entry point for TensileLt. It now returns a named tuple, KernelCodeGenResult, which contains the generated file string and metadata on the code.
• processKernelSource is no longer responsible for writing assembly files or assembling/linking them in any way.
• KernelWriters are now only responsible for generating source code in the form of strings, no more hidden assembler invocations.

Objectives:

• Remove getCompileArgs from KernelWriter
• Remove _getAssembledKernelObjectFile from KernelWriter
• Remove getLinkCodeObjectArgs from KernelWriter
• Remove _getSingleCodeObjectFile from KernelWriter
• Decouple the kernel writer from the link and compile commands altogether
• Move compile and link flag setup currently in TensileInstructions.Utils to the Toolchain module
• Remove the assemble step from KernelWriterAssembly and add it to AssemblyToolchain