[bazel_rule] New DSLX test rule that allows for multiple `compare` options.

[mtdudek]

Right now xls_dslx_test allows only for single compare mode.
This forces user to create 2 or more targets, if they want to
test multiple compare options (see #974).

I'm suggesting adding new xls_dslx_multi_test rule(PR #1012).

[proppy]

Closing following @cdleary suggestion, if this is needed by #1211 it can be implemented as a local https://bazel.build/extending/macros rather than introducing a new rule.