Add definitions for iterator trait.

Address review comments.

Replace typedef ElementId with a struct and simplify getValueForId/getCoordsforId with getValue/getCoords.

In D147011#4228972, @wrengr wrote:

Nit: in the CL summary it should be "Previously, we represented a"

Address review comments.

Fix a comment.

Fixed comment. Rebased. Fixed FileCheck test.

Rebase.

Generate inlined code to compare values.

Add more detail CHECK to FileCheck test.

In D145440#4175722, @aartbik wrote:

any perf results?

The input contains the "meaningfule string for string attr" and followed by comment lines. Do you know why the parser stop in the middle of a comment line?

This change breaks tensorflow test github.com/tensorflow/tensorflow/blob/master/tensorflow/compiler/mlir/tensorflow/tests/compile_mlir_util/mlir-module-serialized-str-attr.mlir

Fix codegen.mlir

Rebase.

Fix comment.

Address review comments: use ASSERT_USIZE_EQ, rename dimRank to lvlRank, fix comments.

Rename d->l, dimInd->dimCoords, prevlvlCoordinates->prevLvlCoords.

Rename I to C, indices to coordinates.

Rename indices to lvlCoordinates, add assert(lvlRank == dimRank && "Rank mismatch").

Remove IsSymmetric in comment.

Split a macro into variadic version and non-variadic version to avoid warnings.

Address review comments.

Avoid writing isSorted with the same value. Add comments to the code.

Trying to fix the build.

Reorder parameters. Rename local nnz to nse. Combines two lambdas.

Update after removing expand_symmetry property. Rename nnz to nse.

Fix doc for symmetry. Fix assembly format.

Address review comment: keep symmetric property, keep two tests with symmetric input with TODO, add to doc about symmetric handling is TBD.

Address review comments.

Rename variables, rank => dimRank, r => d.

Apply clang-format.

Change _sparse_quick_sort to _sparse_qsort. Rebase.

Fix comments to address review feedback.

Rebase.

Rebase.

Rebase.