dbQuoteIdentifier inconsistent with other DBI drivers

[ankane]

Hi, currently, duckdb-r skips quoting identifiers in calls to dbQuoteIdentifier if it's not strictly needed. However, this is inconsistent with other DBI drivers and was surprising as a user (seeing dbQuoteIdentifier not add quotes).

RSQLite     | `test`
RPostgres   | "test"
RPostgreSQL | "test"
RMySQL      | `test`
RMariaDB    | `test`
duckdb-r    | test

Repro script

library(DBI)

show <- function(name, db) {
    cols <- c("test")
    cat(sprintf("%-11s | %s\n", name, dbQuoteIdentifier(db, cols)))
    invisible(dbDisconnect(db))
}

show("RSQLite", dbConnect(RSQLite::SQLite(), dbname=":memory:"))
show("RPostgres", dbConnect(RPostgres::Postgres(), dbname="postgres"))
show("RPostgreSQL", dbConnect(RPostgreSQL::PostgreSQL(), dbname="postgres"))
show("RMySQL", dbConnect(RMySQL::MySQL(), dbname="mysql"))
show("RMariaDB", dbConnect(RMariaDB::MariaDB(), dbname="mysql"))
show("duckdb-r", dbConnect(duckdb::duckdb(), dbdir=":memory:"))