vet: remove false positive space indent errors inside strings (#9568)

cmd/tools/vvet/tests/indent_with_space.out

@@ -1,3 +1,5 @@
 cmd/tools/vvet/tests/indent_with_space.vv:2: error: Looks like you are using spaces for indentation.
 cmd/tools/vvet/tests/indent_with_space.vv:10: error: Looks like you are using spaces for indentation.
+cmd/tools/vvet/tests/indent_with_space.vv:16: error: Looks like you are using spaces for indentation.
+cmd/tools/vvet/tests/indent_with_space.vv:19: error: Looks like you are using spaces for indentation.
 NB: You can run `v fmt -w file.v` to fix these errors automatically

cmd/tools/vvet/tests/indent_with_space.vv

@@ -4,10 +4,17 @@ fn main() {
 
 fn block_comments() {
 	/* tab to indent the comment
-    spaces before
+  spaces before
-    also spaces before
+  also spaces before
-    same here */
+  same here */
-    /* spaces for comment indentation (ouch)
+  /* spaces for comment indentation (ouch)
-    and inside too
+  and inside too
-    */
+  */
+}
+
+fn space_inside_strings() {
+  str := "Bad space usage for variable indentation.
+  Here it's fine.
+  Here too."
+  str2 := 'linebreak and space\n  inside'
 }

vlib/v/parser/parser.v

@@ -2330,9 +2330,14 @@ fn (mut p Parser) string_expr() ast.Expr {
 	}
 	mut node := ast.empty_expr()
 	val := p.tok.lit
-	pos := p.tok.position()
+	mut pos := p.tok.position()
+	pos.last_line = pos.line_nr + val.count('\n')
 	if p.peek_tok.kind != .str_dollar {
 		p.next()
+		if p.vet_errors.len > 0 && val.contains('\n  ') {
+			p.vet_errors = p.vet_errors.filter(!(it.pos.line_nr > pos.line_nr - 1
+				&& it.pos.line_nr <= pos.last_line - 1))
+		}
 		node = ast.StringLiteral{
 			val: val
 			is_raw: is_raw