[frameworks] Do not use light font styles for headings (1/3)

Summary:
This patch turns off light font styles for some headings because they cause visual and legibility issues, as explained in the respective bug report.

BUG: 402730

FIXED-IN: 5.54

Test Plan:
**//Worst case scenario testing//** - font does not have a "light" variant and falls back to using a thinner one such as "hairline"

**Before:**
{F6520036}

{F6520035}

{F6520034}

**After:**
{F6520039}

{F6520038}

{F6520037}

**//Plasma defaults testing//**

**Before**:
{F6520778}

{F6520777}

{F6520776}

**After:**
{F6520781}

{F6520780}

{F6520779}

Reviewers: ngraham, #plasma, #vdg, #frameworks

Reviewed By: ngraham, #vdg

Subscribers: #frameworks, #plasma, #vdg, ngraham, abetts, kde-frameworks-devel

Tags: #frameworks

Differential Revision: https://phabricator.kde.org/D17905

src/declarativeimports/plasmaextracomponents/qml/Heading.qml

@@ -62,8 +62,6 @@ Label {
 
     lineHeight: 1.2
     font.pointSize: headerPointSize(level)
-    font.weight: level <= 4 ? Font.Light : Font.Normal
-    font.styleName: level <= 4 ? "Light" : "Regular"
     wrapMode: Text.WordWrap
 
     function headerPointSize(l) {

src/declarativeimports/plasmaextracomponents/qml/Title.qml

@@ -43,7 +43,5 @@ import org.kde.plasma.components 2.0
  */
 Label {
     id: root
-
-    font.weight: Font.Light
     font.pointSize: theme.defaultFont.pointSize*2
 }