Mostly reindent PHP scripts to spaces.

* PHP-7.3:
  Fix bug #78192 PDO SQLite SegFault when reuse statement after schema has changed

* PHP-7.2:
  Fix bug #78192 PDO SQLite SegFault when reuse statement after schema has changed

Reset stmt->columns when column count changed on new execution of prepared statement

RFC: https://wiki.php.net/rfc/tostring_exceptions

And convert some object to string conversion related recoverable
fatal errors into Error exceptions.

Improve exception safety of internal code performing string
conversions.

This patch removes the so called local variables defined per
file basis for certain editors to properly show tab width, and
similar settings. These are mainly used by Vim and Emacs editors
yet with recent changes the once working definitions don't work
anymore in Vim without custom plugins or additional configuration.
Neither are these settings synced across the PHP code base.

A simpler and better approach is EditorConfig and fixing code
using some code style fixing tools in the future instead.

This patch also removes the so called modelines for Vim. Modelines
allow Vim editor specifically to set some editor configuration such as
syntax highlighting, indentation style and tab width to be set in the
first line or the last 5 lines per file basis. Since the php test
files have syntax highlighting already set in most editors properly and
EditorConfig takes care of the indentation settings, this patch removes
these as well for the Vim 6.0 and newer versions.

With the removal of local variables for certain editors such as
Emacs and Vim, the footer is also probably not needed anymore when
creating extensions using ext_skel.php script.

Additionally, Vim modelines for setting php syntax and some editor
settings has been removed from some *.phpt files.  All these are
mostly not relevant for phpt files neither work properly in the
middle of the file.

Since there is no need to patch libsqlite3 for our purposes, and since
libsqlite3 ≥ 3.3.9 (which is our current requirement) is widely
available on distros, there is no reason anymore to bundle the library.

Besides removing the bundled libsqlite, and adapting the configuration
respectively, we also fix the use of the SQLITE_ENABLE_COLUMN_METADATA
compile time constant to detect whether sqlite3_column_table_name() is
available by a working feature detection (otherwise bug_42589.phpt
would fail).  We also skip bug73068.phpt for libsqlite 3.11.0 to
3.14.1 which have a bug (<https://sqlite.org/src/info/ef360601>).

We also completely drop support for the obscure pdo_sqlite_external
extension (which could have been enabled on Windows only by passing
`--pdo-sqlite-external` to configure), since it is not needed anymore.

Furthermore, we remove references to the bundled libsqlite from
Makefile.gcov, CONTRIBUTING.md and README.REDIST.BINS.

This attribute is a boolean value. It is taken from the return value of
sqlite3_stmt_readonly(), indicating if and only if the prepared statement makes
no direct changes to the content of the database.