DataFrame (Microsoft.Data.Analysis) Tracking Issue

## Summary

This issue tracks priorities and discussions around DataFrame improvements based on issues and feedback.

Microsoft.Data.Analysis Open Issue Query: https://github.com/dotnet/machinelearning/issues?q=is%3Aopen+is%3Aissue+label%3AMicrosoft.Data.Analysis

## Work Items

- [x] #6499
- [ ] #6498
- [ ] #6497
- [ ] #6496
- [x] #6493
- [x] #6494
- [x] #6495

## Related Issues

### Create DataFrames

#### Data Formatting

- [x] #5647
- [x] #6238

#### Data Sources

- [x] #5662
- [ ] #5972
- [ ] #6088
- [ ] #5905
- [ ] #5646

#### Other

- [x] #5968

### Reshape DataFrames

- Pivot / Transpose
- Create columns
- [x] #5670
- Reset indices
- [ ] #5658
- Rename columns
- [x] #6129
- [x] #5916

### Filter / Sort DataFrames

- Filter
- [x] #6110

### Combine DataFrames

- Merge
- [x] #6127
- Join
- [ ] #6128
- [ ] #6133
- Concat
- [ ] #5932
- [ ] #6134

### Group DataFrames

- Grouping
- [ ] #5724
- [ ] #5691
- Aggregate Functions
- [ ] #5681

### Summarize DataFrames

- Descriptive statistics
- [x] #5759

### Handle Missing Data

- Drop missing data
- Impute / Fill missing data

### DataTypes

#### Array / Vector / VBuffer

- [x] #5872
- [x] #5721
- [x] #5746
- [x] #5690

#### DateTime

- [x] #6213
- [x] #6201

#### Other
- [ ] #5898
- [ ] #5656

### Misc

- LINQ / EFCore?
- DateTime operations