feat(sym): Introduce Symbolic Analysis (#45)

(Most of the code is directly copied from `tvm.arith` with very minimal
code change)

This PR establishes a submodule `mlc.sym.`, which does symbolic analysis
and expression simplification for use cases in ML Compilers. It includes
a few pieces:

1) Expression IR (`mlc.sym.expr`): It’s a subset of and thus fully
compatible with TIR. It includes:
- Leaf variables: Var, ShapeVar (nonnegative variables)
- Immediate values: IntImm, FloatImm, BoolImm
- Arithmetics: Add, Sub, Mul, Div, Mod, FloorDiv, FloorMod, Min, Max
- Comparison: EQ, NE, LT, LE, GT, GE
- Logical ops: And, Or, Not
- Vectorization: Ramp, Broadcast, Shuffle
- Others: Cast, Select, Let, Call

2) Analyzer (`mlc.sym.analyzer`): The prover and expression simplifier.
It supports
- `Analyzer.bind`: Bind a `Var` to a certain range, a constant value or
an expression
- `Analyzer.can_prove`: the prover, which is certainly specialized to
bounds we particularly care about in deep learning, e.g. const int
bound. This will not be as powerful as general-purpose solvers such as
Z3, but should suffice for ML compiler use cases (and thus can be
faster);
- `Analyzer.simplify`: the expression simplifier for ML compiler use
cases.

3) `mlc.sym.op`: convenient methods to construct expressions.


Example:

```python
from mlc import sym as S

i0 = S.Var("i0", "int64")
i1 = S.Var("i1", "int64")
i = i0 * 3 + i1
j = i // 12 * 12 + i % 12 // 4 * 4 + i % 4
analyzer = S.Analyzer()
analyzer.bind(i1, S.Range.from_const("int64", 0, 3))
result = analyzer.simplify(j)
print(result)
```

Author: junrushao

CMakeLists.txt

@@ -50,6 +50,14 @@ add_library(mlc_objs OBJECT
   "${CMAKE_CURRENT_SOURCE_DIR}/cpp/c_api.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/cpp/printer.cc"
   "${CMAKE_CURRENT_SOURCE_DIR}/cpp/structure.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/sym.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/text_format.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_const_int_bound.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_modular_set.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_rewrite_simplify.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_canonical_simplify.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_interval_set.cc"
+  "${CMAKE_CURRENT_SOURCE_DIR}/cpp/sym/analyzer_transitive_comparisons.cc"
 )
 set_target_properties(
   mlc_objs PROPERTIES
@@ -63,6 +71,9 @@ set_target_properties(
   MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>DLL"
 )
 add_cxx_warning(mlc_objs)
+if(MSVC)
+  target_compile_options(mlc_objs PRIVATE /bigobj)
+endif()
 target_include_directories(mlc_objs PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/include")
 target_include_directories(mlc_objs PRIVATE "${CMAKE_CURRENT_SOURCE_DIR}/3rdparty/dlpack/include")
 target_link_libraries(mlc_objs PUBLIC mlc::mlc_backtrace-static)