* Update tasks to support incremental build

MonoAOTCompiler:
- Compiles assemblies to .bc files.
- Hashes for the .bc files are stored in a json cache file.
- And uses .depfile generated by mono-aot-cross, to figure out the
  if any of the dependencies have changed
- Writes out the actual .bc file only if the assembly, or it's
  dependencies changed

EmccCompile.cs: Support a `%(Dependencies)` metadata on the source
files, to compile the files only when needed.

* Update wasm targets

* don't pass unncessary args to RunTests

* Add tests for incremental builds

* Disable non-wasm builds, for testing

* Add miggins LogAsErrorException.cs

* Bump sdk for workload testing to 6.0.100-rc.1.21410.3

* fix build

* MonoAOTCompiler: use the full path to copy the final .bc file

* Make the method used with `MemberData`, static

otherwise xunit just shows a cryptic:
```
    Wasm.Build.Tests.RebuildTests.NoOpRebuild [STARTING]
    Wasm.Build.Tests.RebuildTests.NoOpRebuild [FAIL]
      System.NotSupportedException : Specified method is not supported.
```

* add back builds

* Split Wasm.Build.Tests into multiple helix jobs

* Revert "add back builds"

This reverts commit 1d031c04e13780ec73180ba6f06a37ee42c24203.

* Split up native rebuild tests

* remove non-test classes

* add back builds

This reverts commit b008130a7886c2e2b9f16c83641c1b8c936082f6.

* MonoAOTCompiler: make cache optional

* MonoAOTCompiler: handle the case where we have a cache entry, but the file on disk doesn't exist

* Fix aot compiler task output

* MonoAOTCompiler: Use hashes of .bc files instead of assemblies

`--depfile` isn't supported on aot config used by android, and fails
with:

```
* Assertion at /__w/1/s/src/mono/mono/mini/aot-compiler.c:14216, condition `acfg->aot_opts.llvm_only && acfg->aot_opts.asm_only && acfg->aot_opts.llvm_outfile' not met
```

Instead, use hashes of the .bc.tmp files generated, with the existing
.bc files.

* MonoAOTCompiler: Support more than one output file

The earlier implementation assumed that there would be only one output
file. But in some cases (eg. android), there are more than one, like
`.s`, `.dll-llvm.o`.

* -bump sdk for workload testing

* MonoAOTCompiler: don't use tmp files at all, when cache isn't being

.. used.
Co-authored-by: NLarry Ewing <lewing@microsoft.com>