This PR implements the build part of bitmap index support. It follows most of the design described in #1684 , but with the following differences and enhancements
1. Bitmap indexes are now written in the segment file for simplicity. Separate index file would be helpful when we're going to support `alter table add bitmap index` in the future though.
2. We switch to a generalized index page format for all data types rather than specialize for each one. Code simplicity and reusability is preferred here than optimal compression rate.
3. We introduce a new abstraction called `IndexedColumn` to unify the processing of the dictionary section and bitmap section of bitmap index. IndexedColumn is a column with an optional ordinal index and an optional value index. Ordinal index enables us to seek to a particular rowid within the column. Value index requires IndexedColumn to store ordered values and enables us to seek to a particular value. Therefore, the dictionary section can be represented by an IndexedColumn with value index and the bitmap section can be represented by an IndexedColumn with ordinal index.
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