Support Create Index

[PThorpe92]

Closes #1193

│limbo> explain create index idxp on products(price);                                                                                                                        
│addr  opcode             p1    p2    p3    p4             p5  comment
│----  -----------------  ----  ----  ----  -------------  --  -------
│0     Init               0     39    0                    0   Start at 39
│1     CreateBtree        0     1     2                    0   r[1]=root iDb=0 flags=2
│2     OpenWriteAsync     0     1     0                    0
│3     OpenWriteAwait     0     0     0                    0
│4     NewRowId           0     2     0                    0
│5     String8            0     3     0     index          0   r[3]='index'
│6     String8            0     4     0     idxp           0   r[4]='idxp'
│7     String8            0     5     0     products       0   r[5]='products'
│8     Copy               1     6     1                    0   r[6]=r[1]
│9     String8            0     7     0     CREATE INDEX idxp ON products (price)  0   r[7]='CREATE INDEX idxp ON products (price)'
│10    MakeRecord         3     5     8                    0   r[8]=mkrec(r[3..7])
│11    InsertAsync        0     8     2                    0
│12    InsertAwait        0     0     0                    0
│13    SorterOpen         3     1     0     k(1,B)         0   cursor=3
│14    OpenPseudo         4     9     2                    0   2 columns in r[9]
│15    OpenReadAsync      2     273   0                    0   table=products, root=273
│16    OpenReadAwait      0     0     0                    0
│17    RewindAsync        2     0     0                    0
│18    RewindAwait        2     25    0                    0   Rewind table products
│19      Column           2     2     10                   0   r[10]=products.price
│20      RowId            2     11    0                    0   r[11]=products.rowid
│21      MakeRecord       10    2     12                   0   r[12]=mkrec(r[10..11])
│22      SorterInsert     3     12    0     0              0   key=r[12]
│23    NextAsync          2     0     0                    0
│24    NextAwait          2     19    0                    0
│25    OpenWriteAsync     1     1     0                    0
│26    OpenWriteAwait     0     0     0                    0
│27    SorterSort         3     33    0                    0
│28      SorterData       3     13    4                    0   r[13]=data
│29      SeekEnd          1     0     0                    0
│30      IdxInsertAsync   1     13    0                    0   key=r[13]
│31      IdxInsertAwait   1     0     0                    0
│32    SorterNext         3     28    0                    0
│33    Close              3     0     0                    0
│34    Close              2     0     0                    0
│35    Close              1     0     0                    0
│36    ParseSchema        0     0     0     name = 'idxp' AND type = 'index'  0   name = 'idxp' AND type = 'index'
│37    Close              0     0     0                    0
│38    Halt               0     0     0                    0
│39    Transaction        0     1     0                    0   write=true
│40    Goto               0     1     0                    0

This will create the initial index btree and insert whatever relevant records that need to be inserted, it doesn't handle the case of inserting new index keys when normal records are created afterwards. That will prob be added in next PR to keep this one concise.

Limbo will properly use the index in a subsequent query:

Creating a unique index on a column that has 2 existing identical rows:

[pereman2]

TableRowId's record is not really a "key" but the record to insert right? Does it make sense to remain separate to the key?

[PThorpe92]

Yeah this was kind of a pain.. why I included that is because otherwise the arguments to insert would be:

    pub fn insert(
        &mut self,
        key: &BTreeKey,
        record: Option<&ImmutableRecord>,  
        moved_before: bool,
    ) -> Result<CursorResult<()>> {

So making it part of the key felt like ergonomically the best choice.

But indeed, prob at least could use a better name 🤔