[FIX] compiler: fix swapped key/value using t-foreach on Map

In odoo/owl#1352 we added support for using t-foreach on Map objects,
maps should behave the same as objects where keys are available under
the name specified in t-as and values under that same name with the
suffix `_value`. Unfortunately, because the code for objects was written
in a confusing way (values were stored in a variable named `keys` and
vice versa), the implementation for Map was incorrect and keys and
values were swapped.

This commit fixes that and rewrites the code to be less confusing: keys
are extracted from the variables `k_block` and values from `v_block`,
which swaps the behaviour, and the code to prepare a list from an object
now extracts the keys in `keys` and the values in `values`

src/compiler/code_generator.ts

@@ -894,18 +894,18 @@ export class CodeGenerator {
     }
     this.addLine(`for (let ${loopVar} = 0; ${loopVar} < ${l}; ${loopVar}++) {`);
     this.target.indentLevel++;
-    this.addLine(`ctx[\`${ast.elem}\`] = ${vals}[${loopVar}];`);
+    this.addLine(`ctx[\`${ast.elem}\`] = ${keys}[${loopVar}];`);
     if (!ast.hasNoFirst) {
       this.addLine(`ctx[\`${ast.elem}_first\`] = ${loopVar} === 0;`);
     }
     if (!ast.hasNoLast) {
-      this.addLine(`ctx[\`${ast.elem}_last\`] = ${loopVar} === ${vals}.length - 1;`);
+      this.addLine(`ctx[\`${ast.elem}_last\`] = ${loopVar} === ${keys}.length - 1;`);
     }
     if (!ast.hasNoIndex) {
       this.addLine(`ctx[\`${ast.elem}_index\`] = ${loopVar};`);
     }
     if (!ast.hasNoValue) {
-      this.addLine(`ctx[\`${ast.elem}_value\`] = ${keys}[${loopVar}];`);
+      this.addLine(`ctx[\`${ast.elem}_value\`] = ${vals}[${loopVar}];`);
     }
     this.define(`key${this.target.loopLevel}`, ast.key ? compileExpr(ast.key) : loopVar);
     if (this.dev) {