[FIX] t-call-context: make this unavailable in rendering context

t-call-context is a feature that's supposed to mask the rendering
context completely, but currently the component remains available
through `this`.

This commit stops treating `this` as a reserved word, so that it's
compiled to a lookup in the rendering context, and adds `this` to the
rendering context when binding the component's rendering function. With
these changes, `this` behaves the same as before when outside a
t-call-context, but when the rendering context is overriden, the
template can no longer access `this`. `this` still represents the
instance of the component inside of the rendering function since it's
needed by owl internally.

A side-effect of this change is that now the rendering context is no
longer the instance of the component by default, but is always an object
with the component in its prototype chain. This was already the case
before in some contexts (eg inside t-foreach, or inside components with
a t-set/t-call anywhere in its template). This can cause issues in rare
cases when a component method was called directly on the rendering
context, as before this change, the method's bound this would be the
component instance (except in a t-foreach, component with a
t-set/t-call, etc), while after this change it is now never the
component instance. When the method only reads on `this` there is no
issue as all the components properties are available on the rendering
contexts, but setting a value on `this` will write on the rendering
context and not the component which is likely a mistake.

While this is a breaking change, simply adding a t-set/t-call to any
template would break components that would be broken by this change,
with this in mind we decided to make this change anyway so that
developers get the error as early as possible in the development cycle
rather than having a seemingly inocuous change break code under them.

tests/components/__snapshots__/t_call.test.ts.snap

@@ -109,7 +109,8 @@ exports[`t-call handlers are properly bound through a dynamic t-call 2`] = `
   let block1 = createBlock(\`<p block-handler-0=\\"click\\">lucas</p>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    let hdlr1 = [()=>this.update(), ctx];
+    const v1 = ctx['this'];
+    let hdlr1 = [()=>v1.update(), ctx];
     return block1([hdlr1]);
   }
 }"
@@ -168,8 +169,9 @@ exports[`t-call handlers with arguments are properly bound through a t-call 2`]
   let block1 = createBlock(\`<p block-handler-0=\\"click\\">lucas</p>\`);
   
   return function template(ctx, node, key = \\"\\") {
-    const v1 = ctx['a'];
-    let hdlr1 = [()=>this.update(v1), ctx];
+    const v1 = ctx['this'];
+    const v2 = ctx['a'];
+    let hdlr1 = [()=>v1.update(v2), ctx];
     return block1([hdlr1]);
   }
 }"
@@ -287,7 +289,7 @@ exports[`t-call recursive t-call binding this -- static t-call 2`] = `
     ctx[isBoundary] = 1
     let b2;
     if (ctx['level']<2) {
-      let hdlr1 = [\\"stop\\", ctx['onClicked'].bind(this), ctx];
+      let hdlr1 = [\\"stop\\", ctx['onClicked'].bind(ctx['this']), ctx];
       let txt1 = ctx['level'];
       const b3 = block3([hdlr1, txt1]);
       ctx = Object.create(ctx);
@@ -538,7 +540,6 @@ exports[`t-call t-call-context: ComponentNode is not looked up in the context 2`
   let block2 = createBlock(\`<div block-ref=\\"0\\">outside slot</div>\`);
   let block4 = createBlock(\`<div block-ref=\\"0\\">I'm the default slot</div>\`);
   let block5 = createBlock(\`<div><block-text-0/></div>\`);
-  let block6 = createBlock(\`<div><block-text-0/></div>\`);
   
   function slot1(ctx, node, key = \\"\\") {
     const refs = this.__owl__.refs;
@@ -547,11 +548,9 @@ exports[`t-call t-call-context: ComponentNode is not looked up in the context 2`
     ctx[isBoundary] = 1
     const b4 = block4([ref2]);
     setContextValue(ctx, \\"test\\", 3);
-    let txt1 = this.__owl__.name;
+    let txt1 = ctx['test'];
     const b5 = block5([txt1]);
-    let txt2 = ctx['test'];
-    const b6 = block6([txt2]);
-    return multi([b4, b5, b6]);
+    return multi([b4, b5]);
   }
   
   return function template(ctx, node, key = \\"\\") {
@@ -559,8 +558,8 @@ exports[`t-call t-call-context: ComponentNode is not looked up in the context 2`
     const ref1 = (el) => refs[\`myRef\`] = el;
     const b2 = block2([ref1]);
     const ctx1 = capture(ctx);
-    const b7 = comp1({prop: bind(this, ctx['method']),slots: markRaw({'default': {__render: slot1.bind(this), __ctx: ctx1}})}, key + \`__1\`, node, this, null);
-    return multi([b2, b7]);
+    const b6 = comp1({prop: bind(this, ctx['method']),slots: markRaw({'default': {__render: slot1.bind(this), __ctx: ctx1}})}, key + \`__1\`, node, this, null);
+    return multi([b2, b6]);
   }
 }"
 `;
@@ -624,3 +623,27 @@ exports[`t-call t-call-context: slots don't make component available again when
   }
 }"
 `;
+
+exports[`t-call t-call-context: this is not available inside t-call-context 1`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  const callTemplate_1 = app.getTemplate(\`someTemplate\`);
+  
+  return function template(ctx, node, key = \\"\\") {
+    let ctx1 = {};
+    return callTemplate_1.call(this, ctx1, node, key + \`__1\`);
+  }
+}"
+`;
+
+exports[`t-call t-call-context: this is not available inside t-call-context 2`] = `
+"function anonymous(app, bdom, helpers
+) {
+  let { text, createBlock, list, multi, html, toggler, comment } = bdom;
+  
+  return function template(ctx, node, key = \\"\\") {
+    return text(ctx['this']);
+  }
+}"
+`;