Add matchbraceleft option (#3432)

Add `matchbraceleft` option to allow disabling the default behavior
matching not just the brace under cursor but also the brace to the left
of it (which is arguably convenient, but also ambiguous and
non-intuitive). With `matchbraceleft` disabled, micro will only match
the brace character that is precisely under the cursor, and also when
jumping to the matching brace, will always move cursor precisely to the
matching brace character, not to the character next to it.

Nota bene: historical journey:

- There was already a `matchbraceleft` option introduced in commit
  ea6a87d41a, when this feature (matching brace to the left) was
  introduced first time. That time it was matching _only_ the brace
  to the left, _instead_ of the brace under the cursor, and was
  disabled by default.

- Later this feature was removed during the big refactoring of micro.

- Then this feature was reintroduced again in commit d1e713ce08, in
  its present form (i.e. combined brace matching both under the cursor
  and to the left, simulating I-beam cursor behavior), and it was
  introduced unconditionally, without an option to disable it.

- Since then, multiple users complained about this feature and asked
  for an option to disable it, so now we are reintroducing it as an
  option again (this time enabled by default though).

internal/buffer/buffer.go

@@ -1193,17 +1193,19 @@ func (b *Buffer) FindMatchingBrace(start Loc) (Loc, bool, bool) {
 		}
 	}
 
-	// failed to find matching brace for the given location, so try to find matching
-	// brace for the location one character left of it
-	if start.X-1 >= 0 && start.X-1 < len(curLine) {
-		leftChar := curLine[start.X-1]
-		left := Loc{start.X - 1, start.Y}
+	if b.Settings["matchbraceleft"].(bool) {
+		// failed to find matching brace for the given location, so try to find matching
+		// brace for the location one character left of it
+		if start.X-1 >= 0 && start.X-1 < len(curLine) {
+			leftChar := curLine[start.X-1]
+			left := Loc{start.X - 1, start.Y}
 
-		for _, bp := range BracePairs {
-			if leftChar == bp[0] || leftChar == bp[1] {
-				mb, found := b.findMatchingBrace(bp, left, leftChar)
-				if found {
-					return mb, true, true
+			for _, bp := range BracePairs {
+				if leftChar == bp[0] || leftChar == bp[1] {
+					mb, found := b.findMatchingBrace(bp, left, leftChar)
+					if found {
+						return mb, true, true
+					}
 				}
 			}
 		}