Add tvmOnly compilation mode to build

[jeshecdom]

We need to add a compilation mode to build in which compilation stops immediately after the TVM compilation step, i.e., it ignores the packaging, bindings and reports steps. There is currently a funcOnly, but it skips the TVM compilation step on each contract.

Again, this is necessary to avoid copying the code of build for compiling autogenerated ASTs in testing tasks. Related issue: #2343.

[novusnota]

Or bocOnly, because the end result is a .boc file. Plus, we could add some relevant CLI flags, see: #136 (comment)

[jeshecdom]

We reached a temporal solution:

• For the moment, keep the copied build function as done in PR tests: check initOf and codeOf reachability #2083, as this will allow making some optimizations applicable to testing tasks, like compiling only a subset of stdlib. Later, we will have a refactor of build (see PR refactor: build #1363).