Add `lastInsertRowid` to `ResultSet`

[honzasp]

The last inserted rowid is returned from Hrana and HTTP APIs. Let's expose it in the client, too.

The only possible issue is the type of the lastInsertRowid field. There are three options:

• bigint: this is the best way to represent a 64-bit integer in JavaScript, but we don't use bigints anywhere else in the API
• string: we convert JavaScript bigint to SQLite string when storing data into the database
• number: we convert SQLite integers to JavaScript number-s (doubles) when loading data from database, but a number cannot represent all ROWIDs

I decided to go for bigint, because it seems to be least likely to give trouble: it can represent all ROWIDs, and when passed back to SQLite, the client converts it to a string, which SQLite converts back to an integer. (Perhaps it would be better to convert JavaScript bigint to a SQLite integer (and throw an exception if it overflows), but this would break backwards compatibility, so let's do it in the next major release.)

[honzasp]

bors merge

[bors[bot]]

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